'J2 BOTANY AND PHARMACOGNOSY. 



The Gymnosperms represent an ancient group of plants and 

 were more numerous during the Triassic period than now. They 

 are mostly shrubs and trees, and do not shed their leaves period- 

 ically as the Angiosperms do, and hence are known as " ever- 

 greens." As in some of the Pteridophytes {Lycopodimn, Eqid- 

 setum) the sporophylls occur in groups forming cones or strobiles 

 (Fig. 47). They not only differ in external appearance from the 

 Angiosperms but also in the anatomical structure of the stem, 

 which is without large conducting vessels. In order to understand 

 the relation of the Gymnosperms to the Pteridophytes on the one 

 hand and to the Angiosperms on the other, it will be necessary to 

 consider briefly the life history of a representative group, such as 

 the Coniferse. 



General Characters. The seed consists essentially of three 

 parts, namely, a woody or leathery seed-coat, a nutritive layer 

 rich in oil known as the endosperm, and a straight embryo. The 

 latter is a more or less differentiated plantlet, consisting of a stem 

 with a varying number of cotyledons or first leaves (2 to 16), 

 and a small root which is attached to a suspensor, as is the embryo 

 in Selaginella (Fig. 44). AVhen the embryo begins its develop- 

 ment into the plant it uses up the nourishment with which it is 

 surrounded in the endosperm, and as it increases in size the seed- 

 coat is split. The root then protrudes and the cotyledons to some 

 of which the seed-coat is still attached are carried upward by the 

 stem through the surface of the soil, when the seed-coat is cast 

 off and the plant begins an independent existence. The first root 

 is the primary or tap root and from this are sent out numerous 

 branches known as secondary roots, constituting a well developed 

 root system which serves the double purpose of absorbing nutri- 

 ment from the substratum or soil and of holdins: or fixinsf the 

 plant in its upright position. The embryonal stem grows ver- 

 tically upwards continuing its growth indefinitely. Lateral 

 branches arise at more or less regular intervals which extend from 

 near the ground to the apex, the younger branches continually 

 succeeding the older ones from the ground upward, thus giving 

 the trees a cone-like outline. The leaves arise on the branches 

 and are of two kinds, primary leaves which are more or less scale- 

 like and deciduous, and secondary leaves which are true foliage 



