90 BOTANY AND PHARMACOGNOSY. 



oospore develops at once into the embryo' or plantlet as seen in 

 the seed, this stage being followed by a period of rest. In fact 

 the young plant may lie dormant in the seed for years. 



Development of Seed. — The steps in the development of 

 the mature seed occur in the following order (Fig. 57); The 

 oospore divides into two parts, an upper portion which gives rise 

 to the embryo, and a lower portion which by transverse segmenta- 

 tion gives rise to a short suspensor (Fig. 57, v) which practically 

 serves the same purpose as in the Gymnosperms (page 78). 

 The embryonal cell develops the embryo which consists of: (i) 

 a root portion which is connected with the suspensor (Fig. 57, w) ; 

 (2) one or two cotyledons (Fig. 57, c) which are attached to the 

 stem ; (3) a little bud at the apex of the stem which is known as 

 the plumule. 



While the embryo is developing, the nucleus of the embryo- 

 sac, either after fusing with the prothallial cell of the pollen 

 grain, or in the absence of such union, begins active division, 

 forming a highly nutritive tissue rich in starch, oil, or proteids, 

 known as the endosperm (Figs. 121 and 122). Simultaneously 

 with the development of the endosperm the nucellus may give 

 rise to a nutritive layer called the perisperm, or the tissues of 

 the nucellus may be rnodified and form with the altered integu- 

 ments or coats of the ovule, the seed-coat. 



Jnasmuch as the Angiosperms furnish by far the larger pro- 

 portion of plants and plant products used in medicine, it is desir- 

 able to give particular attention to the morphology of the plant 

 as also to the distinguishing characters of a number of the impor- 

 tant groups or families. 



Economic Importance. — As indicating the great usefulness 

 to rriankind of the products obtained from the Angiosperms it 

 will be sufficient to merely mention that all of our garden vegeta- 

 bles as well as the great crops of cereals like wheat, corn, rye, 

 etc. ; edible fruits and seeds ; textile products, such as cotton, flax, 

 etc. ; medicinal products ; timbers of various kinds, as oak, mahog- 

 any, walnut, chestnut, cherry, etc., are furnished by this great 

 group of plants. 



