LESSON 3.] GROWTH OF THE PLANT FROM THE SEED. 



13 



to the first leaves that appear. In most cases of the sort, the radicle, 

 or short original stemlet of the embryo be- 

 low the cotyledons (which is plainly shown 

 in the Pea, Fig. 19), lengthens very little, 

 or not at all ; and so the cotyledons remain 

 under ground, if the seed was covered by 

 the soil, as every one knows to be the case 

 with Peas. In these (Fig. 20), as also in 

 the Oak (Fig. 22), the leaves of the first 

 one or two joints are imperfect, and mere 

 small scales ; but genuine leaves immedi- 

 ately follow. The Horsechestnut and Buck- 

 eye (Fig. 23, 24) furnish another instance 

 of the same sort. These trees are nearly 

 related to the Maple ; but vphile the seed- 

 leaves of the Maple show themselves to 

 be leaves, even in the seed (as we have 

 already seen), and when they germinate 

 fulfil the office of ordinary leaves, those 

 of the Buckeye and of the Horsechestnut 

 (Fig. 23), would never be suspected to be 

 the same organs. Yet they are so, only 

 in another shape, — exceedingly thickened 

 by the accumulation of a great quantity 

 of starch and other nourishing matter in 

 their substance ; and besides, their contigu- 

 ous faces stick together more or less firmly, 

 so that they never open. But the stalks 

 of these seed-leaves grow, and, as they 

 lengthen, push the radicle and the plumule 

 out of the seed, when the former develops, downwardly the root, the 

 latter upwardly the leafy stem and all it bears (Fig. 24). 



" 30. Deposit of Pood outside of the Embryo. Very often the nourish- 

 ment provided for the seedling plantlet is laid up, not in the embryo 

 itself, but around it. A' good instance to begin with is furnished by 

 the common Morning-Glory, or Convolvulus. The embryo, taken 

 out of the seed and straightened, is shown in Fig. 26. 'it consists 

 of a short stemlet and of a pair of very thin" and delicate green 

 leaves, having no stock of nourishment in them for sustaining the 



FIG. 91. An acorn divided lengthwise. 92. The germinating Oak, 



