ii. 124

Gorgoniidæ, structure and mode of reproduction of, ii. 123, 124 the three natural groups of, ii. 124

Gracilaria compressa, i. 239

Gracilaria lichenoides, or Ceylon moss, i. 239

Gracilaria armata, mode of reproduction of, i. 230

Graminaceæ, structure and mode of reproduction of, i. 385, 386

Grammatophora serpentina, structure and development of, i. 197

Graphidei, characters of the order, i. 308 habitat of the, i. 309

Graphite, form of the crystals of, i. 15 natural, little or no porosity of, i. 112 porosity of artificial graphite, i. 112

Grasses, silica in the stalks and leaves of the, i. 17

Grasses, structure and mode of reproduction of, i. 385-387

Gravitation, force of, less powerful than that of molecular attraction,