SECTION 3.] 



SEEDLINGS. 



17 



urination. The larger the supply to draw upon, the stronger the growth, 

 and the quicker the formation of root below and of stem and leaves above. 

 This deposit of food thickens the 

 cotyledons, and renders them less 

 and less leaf-like in proportion to 

 its amount. 



24. Examples of Embryos 

 with thickened Cotyledons. 

 In the Pumpkin and Squash (Fig. 

 26, 27), the cotyledons are well 

 supplied with nourishing matter, 

 as their sweet taste demonstrates. 

 Still, they are flat and not very 

 thick. In germination this store 

 is promptly utilized in the devel- 

 opment of the caulicle to twenty or 

 thirty times its length in the seed, 

 and to corresponding thickness, in 

 the formation of a cluster of roots 

 at its lower end, and the early pro- 

 duction of the incipient plumule ; 

 also in their own growth into effi- 

 cient green leaves. The case of 

 our common Bean (Phaseolus vul- 

 garis, Pig. 28-30) is nearly the 

 same, except that the cotyledons 

 are much more gorged ; so that, although carried up into the air and light 

 upon the lengthening caulicle, and there acquiring a green color, they 

 never expand into useful leaves. Instead of this, they nourish into rapid 

 growth the plumule, which is plainly visible in the seed, as a pair of 

 incipient leaves ; and these form the first actual foliage. 



25. Very similar is the germination of the Beech (Pig. 31-33), except 

 that the caulicle lengthens less, hardly raising the cotyledons out of the 

 ground. Nothing would be gained by elevating them, as they never grow 

 out into efficient leaves ; but the joint of stem belonging to the plumule 

 lengthens well, carrying up its pair of real foliage-leaves. 



26. It is nearly the same in the' Bean of the Old World (Vicia Paba, 

 here called Horse Bean and Windsor Bean) : the caulicle lengthens very 

 little, does not undertake to elevate the heavy seed, which is left below or 



Fig. 21. Fruit (one key) of Silver Maple, Acer dasycarpum, of natural size, the 

 seed-bearing portion divided to show the seed. 22. Embryo of the seed taken 

 out. 23. Same opened out, to show the thick cotyledons and the little plumule 

 or bud between them. 24. Germination of Silver Maple, natural size; merely the 

 base of the fruit, containing the seed, is shown. 25. Embryo of same, taken out 

 of the husk; upper part of growing stem cut off, for want of room. 



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