xxviu 



INTRODUCTORY LESSONS. 



There are many other names applied to 

 fruits, which it is not necessary to define 

 here. 



The Gro-wth of Ovules. You can 



not study the development of ovules from the 

 beginning, without the help of a compound 

 microscope, but you can easily observe all 

 stages of growth, from a tiny green speck 

 to the full-grown embryo. Most seeds are 

 nearly full grown in appearance before the 

 embryo is more than fairly visible to the 

 naked eye. The seed coat, filled with a 

 syrupy or milky, usually sweet, liquid, ap- 

 jjears to constitute the very young seed. 

 With a sharp knife cut in halves a great 

 many green peas, in size from half grown 

 7 J upward. You will surely find in some of 



them tiny green embryos, and you may get specimens from the size of a 

 pin's head up to those which tightly fill the seed coat. In Fig. 75, at the 

 top, is seen — magnified two diameters — the young seed of a lupine, cut so 

 as to show the young embryo lying in one end. In the same figure is 

 represented a radish pod, laid open so as to show three of the seeds, two 

 of which exhibit their partly grown embr}'os.* Below, at b, is one of 

 these magnified, and at a an older one, also magnified. The grown em- 

 bryo completely fills the seed. Observe the positions of the embryos in 

 relation to the stems of the seeds and the. stems of the pods. The lower 

 seed in the radish is fastened to the lower side of the pod, the middle 

 seed grows to the upper side. The cotyledons increase much more in 

 size than the radicle. The embryo evidently grows, in part at least, by 

 absorbing the liquid around it. Suppose the embryo of the lupine to quit 

 growing at the size represented in the figure, and that the liquid around 

 it thickens until it becomes solid. Would not the seed thus formed be 

 albuminous ? 



* These are cut in two. The embryo may be Been through the seed-coat, as represented at 6, by hold 

 ing it up to the light. Half of the seed-coat is removed from a. 



