STRUCTURE OF THL FLOWER. 263 



tions. A flower, when complete, is made up of organs which 

 arc usually grouped in two classes, — the outer, which are 

 protective, and which often attract insects ; and the inner^ 

 which are directly concerned with reproduction. The latter 

 class of organs consists of two kinds, — the stamens and the 

 pistil. The stamens are the male, the pistil the female or- 

 gan of the flower. The stamens contain fertilizing grains of 

 pollen, — a substance which in some flowers is dry as dust, 

 in others more or less coherent. The pistil is composed of 

 a hollow closed case (the ovary containing the ovules), which 

 is surmounted by a sticky knob or line (the stigma), not 

 unfrequently upon a slender prolongation of the ovary (the 

 style). The ovules are minute bodies which possess at one 

 part an embryonal vesicle, or tiny mass of protoplasm, in a 

 compartment or cell, generally larger than the other cells 

 of the ovule, and known by the name of embryonal sac. 

 When, as explained last year in the lecture on hybridization, 

 pollen of the right kind and at the proper time falls upon 

 the stigma, it sends down, sooner or later, a microscopic tube, 

 which makes its way to the embryonal sac of the ovule. As 

 a result of the contact, a series of changes begins in the 

 embryonal vesicle. The changes which are thus initiated by 

 the pollen may go on to completeness in the formation of a 

 ripe, sound seed; but the changes may stop far short of 

 this, in wliich case an imperfect seed must necessarily result. 

 At the time of or shortly after fertilization of the embryo- 

 nal vesicle, certain changes take place also in the ovary, and 

 sometimes in the surrounding parts. The fertilized ovary, 

 often with adhering parts which have become likewise modi- 

 fied, becomes the fruit. 



If the fruit ripens with only one seed within, it may so 

 closely resemble a seed in its appearance, that it may be mis- 

 taken for one, and called a seed. For instance, the seeds of 

 wheat and the other cereals, of buckwheat, beet, sunflower, 

 parsnip, and carrot, are all contained in fruits, or ripened 

 ovaries ; and, although such are cases of true fruits, they are 

 popularly termed seeds, and are generally so denominated in 

 treatises upon agricultural seeds. 



A seed consists of its own integuments, or coats, and a 

 nucleus, or kernel. The intcgaments difi'er greatly in rex- 

 ture in seeds of different plants, and somewhat, as will be 

 seen farther on, in seeds of the same kind. 



