Part 23

If we pass from these to the order PINOIDEÆ, we find the female flowers collected into catkin-like cones, which have been considered from various points of view to be sometimes single flowers, at other times compound inflorescences. The structure in ABIETACEÆ is as follows: a number of spirally arranged, scale-like leaves, _cover-scales_ (Figs. 267, 268), are situated on a long axis. In the axil of each cover-scale a larger leaf-like projection, _the ovuliferous scale_, is borne, which turns the upper side towards its cover-scale (which is shown by the fact that the wood of its vascular bundles is turned downwards and towards the wood in the bundles of the cover-scale: Fig. 269). Two ovules, with micropyles turned towards the central axis, and with apparently only one integument (Fig. 268), are situated on the dorsal side of each ovuliferous scale, _i.e._ the side turned away from the cover-scale. The ovuliferous scales grow after fertilisation, into the woody or leathery “cone-scales,” which are usually much larger than the cover-scales. This ovuliferous scale with its axis may, according to Celakovsky, be considered as a dwarf-branch which is situated in the axil of the cover-scale, and bears two ovules (in the same way as in _Ginkgo_, one long-stalked flower, reduced to two ovules, is situated in the axil of a leaf), and _in this case the external integument of the ovules_ is expanded into leaf-like bodies, which have united to form one “_symphyllodium_” (_ovuliferous scale_) which is inverted so that its dorsal side is turned upwards and bears the nucellus and the other integument (“hemichlamydeous” ovules). The carpel itself is therefore in this instance extremely reduced. The keel, or (in _Pinus_) “mucro” (Fig. 268 _B_), which is found in several genera, represents then a third carpel, which is sterile. In the other orders of the Pinoideæ the cover-scales and ovuliferous scales grow more and more together and finally form one structure, which also is termed a “cone-scale,” although from its development it cannot be homologous with the cone-scales of the Abietaceæ. This connation is least in the TAXODIACEÆ and ARAUCARIACEÆ and may be traced on the upper surface of the “cone-scale” by the presence of a stronger or slighter ridge or pad, the free portion of the ovuliferous scale (Figs. 256, 266, 269). It is most strongly pronounced in the CUPRESSACEÆ, in which the two scales form one single structure, the cone-scale (Fig. 274). The vascular bundles in the under portion corresponding to the cover-scale, have the xylem towards the upper side as usual in leaves, whilst the bundles present in the upper side of the cone-scale, which thus represents the ovuliferous scale, turn their xylem downwards. The hemichlamydeous ovules are then situated on the upper side of this cone-scale. According to this theory the CUPRESSACEÆ appear to be the youngest type, a view which corresponds with their vegetative structure. If there is only one ovule in these orders as in _Agathis_ (Fig. 265) and _Araucaria_, then the flower is reduced to a single carpel and one ovule, as in the case of _Dacrydium_ and _Microcachrys_. If two or more ovules are present, then the same number of carpels may be supposed to exist, the external integuments of their ovules being developed into leaf-like structures which collaterally coalesce to form a “symphyllodium,” or are suppressed.

According to this theory, which is based on the researches of Celakovsky, the female flowers of the Coniferæ may be classed thus:--

1. In all cases situated in the axil of a bract and collected into cones, with numerous flowers or with few or one flower. In _Ginkgo_ only, are they situated in the axil of foliage- or scale-leaves.

2. It is only in _Taxus_ that bracteoles are present.

3. They are formed only from rudimentary carpels, in which the stem takes no part.

4. The number of carpels in each flower varies from one to many, most frequently three, of which the central one remains sterile.

5. Each carpel bears only one ovule. The flower which is formed of only one carpel appears to consist of only one ovule.

6. The ovule has in Taxaceæ either a double integument (Podocarpeæ, Taxeæ), of which the external is the “aril,” or, as in the Cycadeæ, a single one, which is homologous with the two united together.

7. The external integument in the Pinoideæ is expanded to form a leaf-like structure--the ovuliferous scale--and bears on its dorsal side the ovules, which are thus only provided with one, and that the inner, integument.

This later interpretation of the female cones in the Coniferæ is more probably correct than the older ones; that, however, which appeared in the former issues of this book, may also be stated. It was to the effect that each catkin-like female cone is in reality a single flower; the cone-scales in the Cupressaceæ were single leaves, namely carpels, which bore the ovules on the side which is turned upwards; the division into two parts which makes its appearance in the other orders, and becomes most prominent in the Abietaceæ, was compared with the division of a leaf into a barren and a fertile portion, which is found especially in Ophioglossaceæ and Marsiliaceæ, or with the ligule in _Isoëtes_.

POLLINATION is accomplished by means of the wind. At the period of pollination the leaves are always so widely separated from one another, that the ovules can catch the pollen-grains carried to them by the wind; this is often effected by the mucilaginous drops which appear at the micropyle, and by the evaporation of which the pollen-grains are brought in contact with the nucellus. The entire cone grows considerably as soon as fertilisation has taken place, and the cone-scales in Pinoideæ close together so that the seeds while maturing are enclosed, and it is not until the seeds are ready for distribution that the cone-scales again become separated. In the Pinoideæ, the fully developed ovuliferous scales are hard and woody; and in this condition the collection of female flowers is termed a _cone_. In the Taxoideæ, true cones are the exception. 2–15 cotyledons are present, arranged in a whorl.

The characteristic feature of this class is the abundance of _resin_, which is to be found in isolated cells (especially in the cortex), partly in intercellular glands or passages (both in the cortex and wood). _Taxus_ is the only genus which has no resin.

There are about 350 species, mostly from the Northern Temperate zone (especially North America and Siberia), where they grow gregariously and form the most northern forests. The Juniper, Scotch Fir, and Yew are natives of Great Britain.

This class may be divided into two families:--

1. =Taxoideæ.= The ovules have either one integument, the external part of which is fleshy, and the internal hard and stone-like; or two integuments, of which the external is the fleshy and coloured “aril.” “Ovuliferous scales” are wanting. The cones are never woody, but are generally succulent, the bracts become fleshy, or cones usually are not developed. The seeds project more or less freely beyond the bracts.

2. =Pinoideæ.= The ovules have two integuments, the external one of which is leaf-like and becomes developed as the “ovuliferous scale”; if there are several of these in each flower they unite and form a “symphyllodium.” This may remain free or unite with the bract. The cones are most frequently woody, rarely succulent. The seeds are hidden among the cone-scales.

Family 1. =Taxoideæ.=

This family, considered to be most nearly related to the Cycadeæ, also made its appearance at a very early period. There is only one order.

Order. =Taxaceæ.= The characters have been given above.

_A._ CEPHALOTAXEÆ is the oldest group, presumably the connecting link between the Cycadeæ and the other Coniferæ. The flower consists normally of two ovules. Aril wanting. One integument. Seeds drupaceous.--The flowers in _Ginkgo biloba_ (_Salisburia_) are situated in the axil of foliage- or scale-leaves. The stamens bear only two pollen-sacs (Fig. 260 _A_). The female flower has two ovules, placed together at the end of a long, bare axis (Fig. 260 _C_). Round the base of the ovule a small collar (_ar_, in Fig. 260 _D_) is found, which may probably be considered homologous with the collar-like outgrowth which surrounds the base of the _Cycas_-ovule. The seed resembles a Plum, and has a fleshy external coat, surrounding a hard internal layer. The embryo is developed after the seed has fallen off. The Ginkgo-tree has long-stalked, fan-shaped leaves, more or less indented, with dichotomous veins resembling certain Ferns--the Adiantums. It is a native of East Asia, and the only surviving species of a genus which in earlier times was very rich in species, and distributed over the entire Northern Hemisphere. _Cephalotaxus_ (Eastern Asia) is related to it.

_B._ PODOCARPEÆ. The female flower is reduced to one ovule, placed in the axil of a bract, or a little forward upon it. The ovule has an aril (2 integuments).--_Phyllocladus_ (Fig. 261), from New Zealand and Tasmania, has obtained its name from its flat, _leaf-like branches_, the leaves proper being scale-like (_f_). The ovules stand _erect_ in the axil of the scale-like leaves (_c_), and several are collected at the end of short branches.--_Microcachrys tetragona_ (Tasmania) has a small female catkin with several spirally-placed, fleshy bracts, at the end of which the inward and downward turned ovule is attached (Fig. 262 _A_, _A’_). The ripe cones are red, succulent, and resemble Strawberries.--In _Dacrydium_ (Tasmania, New Zealand, Malaysia) the female cone has most frequently only 1–2 (–6) bracts, which resemble the vegetative leaves; they have also a fleshy aril (Fig. 262 _B_, _B’_).--_Podocarpus_ (40 species, East Asia, S. Temp.); the bracts of the female flowers become fleshy, and unite together; only 1 or 2 are of use in supporting the flowers. The ovules project high above the apex of the bract, and are _anatropous_, the micropyle being turned downwards (Fig. 262 _C_, _D_). An aril commences to develope in the flowering period as an external coating, and later on it becomes fleshy and coloured.

_C._ TAXEÆ. The female flower is reduced to one ovule, which is situated _terminally_ on an axis which bears 2–3 pairs of opposite, scale-like bracteoles; on this account the Taxeæ form a very isolated group among the Coniferæ.--_Taxus_ (_T. baccata_, the Yew-tree). _Diœcious_. _The female flower consists of only one ovule_, placed _at the end_ of a short secondary branch (Fig. 264), which is studded with scale-like leaves. The aril when ripe is thick, fleshy, and scarlet (sometimes yellow), and only loosely envelopes the seed (Fig. 263). The leaves are scattered, flat, linear, and pointed (Fig. 263, 264). The short male flowers have 5–8 pollen-sacs, pendent from the stamens, and are surrounded at their bases by scale-like bracteoles (Fig. 243). _Torreya_ (4 species, N. America and Japan) is closely allied to _Taxus_. The aril ultimately fuses with the woody inner integument, and hence the ovule becomes drupaceous, as in Cephalotaxaceæ.

USES. _Taxus baccata_ is usually planted in gardens, especially in hedges. Its wood is very hard and is used for wood-carving. The shoots are poisonous, but not the aril, which is often eaten by children and by birds.

Family 2. =Pinoideæ.=

The four orders differ from one another partly in the arrangement of the leaves (_Cupressaceæ_ have opposite or verticillately placed leaves, flowers, and inflorescences; in the others they are placed spirally), but chiefly in the greater or less degree of union which takes place between the female flower (the leaf-like “symphyllodium”) and its supporting cover-scale, and in the position of the ovules (the micropyle being turned upwards or downwards). The “cone-scales” in _Abietaceæ_ are formed by “symphyllodia” alone, in the others by their union with the cover-scale.

Order 1. =Araucariaceæ.= This order most frequently has _solitary_ ovules, _turned downwards_ and attached _to the centre_ of the cone-scales. In _Agathis_ (_Dammara_) the arrangement is the most simple, a winged seed (Fig. 265), which hangs _freely_ downwards, being borne in the centre of the undivided cone-scale. In _Araucaria_, the stamens with the _free, pendulous_ pollen-sacs have been represented in Fig. 242; the ovuliferous scale is united for nearly its whole length with the bract, and projects from its apex in the shape of a sheath-like, dentate scale, resembling the ligule in _Isoëtes_, and may therefore be termed a “ligule.” _Araucaria_ (S. America, Australia) has often rather broad leaves (_A. brasiliensis_). The ovuliferous scale in _Cunninghamia_ is more distinct, and stretches transversely over the entire cover-scale; it bears three inverted ovules (Fig. 266) (Eastern Asia).

Dammara-resin, which is used for varnish, is obtained from _Agathis_ (_Dammara_) species (New Zealand, Philippine Islands).

Order 2. =Abietaceæ (Pine and Fir Trees).= The leaves are spirally arranged and needle-like. The flowers are _monœcious_. The male flowers are long, and catkin-like, with numerous stamens, each bearing two _oblong pollen-sacs_. The pollen-grains are most frequently tri-lobed, having two bladder-like appendages, formed as outgrowths of the exospore, to assist in their distribution by the wind (Fig. 267 _N_). The bracts are arranged spirally. The union between the bract and the ovuliferous scale, which is found in the preceding order, is not in this instance so complete; these scales make their appearance as two free parts, and are attached only at their bases (Fig. 268); the lower portion, that is the cover-scale, in most instances remains quite small (Fir, Red Pine, and others), it is only in the “Noble Pine” (_Abies_) and _Pseudotsuga douglasii_, that it attains a greater length than the ovuliferous scale (Fig. 267, _B-G_). On the other hand the upper part, _the ovuliferous scale_ (the vascular bundles of which have the bast turned upwards), grows strongly and elongates, especially after fertilisation, becoming woody or leathery; it is commonly termed the “_cone-scale_,” but is in reality only homologous with a part of the “cone-scale” in the other order of Pinoideæ. On the side of the ovuliferous scale, turned towards the axis, are situated _two ovules_ with micropyles _directed inwards_. The seeds are most frequently provided with _a false wing_ (a tissue-like part of the surface of the ovuliferous scale). Cotyledons, _more than_ 2, _verticillate_. _Fertilisation does not take place until some time after pollination._ In _Pinus_, for instance, the pollen-tube only penetrates the nucellus for a short distance during the year of pollination, and then ceases its further growth, fertilisation not taking place until after the middle of the next year; whilst the seeds ripen about a year and a half after pollination. In the Larch and others, the seeds are mature in the autumn succeeding pollination.

_Abies_ (Fir). The leaves are often (_e.g. Ab. pectinata_) displaced into 2 rows, flat and indented at the apex, with 2 white (wax-covered) lines on the under surface, in which the stomata are situated. The leaf-scars are nearly circular and do not project. The cones are erect. _The cover-scales and the ovuliferous scales separate from the axis_, to which they remain attached in other genera.--~_Tsuga_ has leaves like _Abies_, but by the slightly projecting leaf-scars, and cones with persistent scales, it forms the transition to _Picea_.--_Pseudotsuga_ has leaves similar to those of _Abies_ and persistent carpels as in _Picea_, but the cover-scales grow as in _Abies_ and project beyond the ovuliferous scales (_P. douglasii_, Fig. 267). These two genera are considered as sub-genera of _Abies_.~--_Picea_. The leaves project on all sides, square and pointed; the leaf-scars are rhombic, on projecting leaf-cushions. The cones are pendulous. The cover-scales are much shorter than the leathery, persisting ovuliferous scales.--The genus _Larix_ (Larch) differs from all the others in having deciduous leaves (the three preceding have leaves which persist for eleven to twelve years). It has _long-branches_ with linear foliage-leaves and short, thick, _perennial dwarf-branches_, which each year form a new rosette of foliage-leaves, similar to those on the long-branches. The male flowers and the erect cones resemble those of _Picea_, and are borne on dwarf-branches.--_Cedrus_ (Cedar) resembles _Larix_ to some extent, but has persistent leaves (_C. libani_, _C. deodara_).--_Pinus_ (Pine) has long-branches and dwarf-branches. The leaves of the long-branches are scale-like and not green; the dwarf-branches have very limited growth, and persist for three years; they arise in the axils of the scales borne on the long-branches of the self-same year, and each bears 2–5 foliage-leaves, they are also surrounded at the base by a number of membranous bud-scales. The cone-scales have a _thick, rhomboid extremity_ (the “shield”).

The buds which develope into long-branches arise at the apex of other long-branches, and being very close together, form false whorls. The female cones occupy the position of long-branches, and take about two years for their development. The male flowers arise close together, and form a spike-like inflorescence at the base of a long-branch of the same year. The male flowers occupy the position of dwarf-branches, so that a female cone may be considered to be a modified long-branch, and a male cone a modified dwarf-branch. The main axis of the seedling has needle-like leaves, similar to those found on the older parts, and on dwarf-branches; it is not until some time later that the dwarf-branches are developed and the permanent arrangement attained.

USES. Several species are commonly cultivated in this country, partly on heaths and moors, and partly in plantations and as ornamental trees, such as Mountain Pine (_Pinus montana_, Cen. Eur.); Austrian Pine (_P. laricio_, Eur.); Scotch Fir (_P. silvestris_, Eur.); Weymouth Pine (_P. strobus_, N. Am.); common Red Pine (_Picea excelsa_, Cen. and N. Eur.); White Pine (_P. alba_, N. Am.); _Abies pectinata_ (Common Fir, S. and Cen. Eur); _A. nordmanniana_ (Crimea, Caucasus); _A. balsamea_ (N. Am.); _Tsuga canadensis_ (N. Am.); _Pseudotsuga douglasii_ (N.W. Am.); Larch (_Larix europæa_, Alps, Carpathians); _L. sibirica_ (N.E. Russia, Siberia).--The wood of many species, especially Pine, on account of its lightness and because it is so easily worked, is very well adapted for many useful purposes. The wood of the Yew-tree is very hard and is used for ornamental turning. Resin and Turpentine (_i.e._ Resin with essential oils, the name being derived from the Terebinth-tree, from which formerly a similar material was obtained) are extracted from _Pinus laricio_ and _P. pinaster_. Oil of Turpentine is obtained by distillation of turpentine with water; Tar by dry distillation of Pine-wood. Canada-balsam is from North American _Abies_-species (_A. balsamea_ and _Fraseri_). The officinal Turpentine is mainly obtained from _Pinus pinaster_ (South of France), _P. tæda_, _australis_, _strobus_ (Weymouth Pine) and other North American species; more recently also from _P. silvestris_ (Scotch Fir), _maritima_, _laricio_, _Picea excelsa_, and others; Venetian Turpentine, from Larch (S. Eur.) Amber is resin from a Tertiary plant (_Pityoxylon succiniferum_), closely related to the Pine, which grew especially in the countries round the South-East coast of the Baltic. _Pinus pinea_ (the Pine, S. Eur.) has edible seeds and also _P. cembra_ (in Cen. Eur. and Siberia).

Order 3. =Taxodiaceæ.= The vegetative leaves and cone-scales are arranged spirally. The ovules (2–9) are situated either at the base of the ovuliferous scales, in which case they are erect; or at their centre, when they are generally more or less inverted. The ovuliferous scale is more or less united with the cover-scale, and projects beyond the surface of the cone-scale, like a comb (Fig. 269). The vascular bundles, which extend into the cover-scale, have the usual leaf-arrangement, viz. the wood placed above the bast; while those bundles which enter the ovuliferous scale have this arrangement of the bundles reversed.