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, %v) ; 

 (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 proteins, 

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

 with the development of the endosperm the nucellus may give 

 rise to a n\itritive layer called the perisperm, or the tissues of 

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

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



Inasmuch 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 mankind 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, cliestnut, cherry, etc., are furnished by this great 

 group of plants. 



