OF THE EMBRYO AND SEEDLLMJ. 



17 



dons, i. e. cotyledons well charged with nourishing matter. The 

 early vegetable physiologists gave to it the name of PLUMULE 

 (Lat. plumula, a little plume). The 

 name was suggested by its appearance 

 in such an embryo as that of the bean 

 (Phaseolus), in which it evidently con- 

 sists of a rudimentary pair of leaves, 

 while in the pea and the acorn it is a 

 rudimentary stem, the leaves of which 

 appear only later, when germination 

 has considerably advanced. In any 

 case, the plumule is the bud of the 

 ascending axis already discernible in 

 the seed. Fig. 27, a, shows it in the 

 almond, one cotyledon being removed. 

 Fig. 28 shows it in the section of a 

 similar although much smaller embryo, 

 that of an apple-seed, enlarged to 

 nearly the size of the other. It is 

 equally visible in the cheriy, the bean, 

 and the beechnut. The embryo in all 

 these cases constitutes the whole kernel 

 of the seed. For the nourishment, 

 which in all the foregoing illustrations 

 except the first (i.e. in Fig. 13, 17-23), 

 is deposited around or exterior to the 

 embryo, is in these stored within it. 



31. The development of these em- 

 biyos in germination proceeds in the 

 normal manner, but with two cor- 

 related peculiarities. First, by the 

 lengthening of the radicle more or less, their thick cotyledons 

 are usually raised to or above the surface of the soil ; the}- 

 expand, assume the green color needful to foliage ; but they 

 imperfectly or in a small degree perform the function of 

 green leaves. Their main office is to supply the other growing 

 parts with the prepared nourishment which they abundantly 

 contain. Then, being thus copiously nourished, the root below 

 and the ready-formed plumule above grow rapidly and strongly, 

 having accumulated capital to draw upon ; and the leaves of the 



FIG. 31. Beechnut cut across, filled by the fleshy embryo; the thick cotyledons 

 partly enfolding each other. 32. Embryo of the same in early germination 33. Same 

 more advanced ; the plumule, which is just emerging in the preceding, here developed 

 into a long iiiternode and a pair of leaves. 



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