11.] THE BEAN-PLANT. 69 



icleus. The nucleus contains a sac, the embryo sac, in 

 hich certain cells, one of which is the emhryo cell, and 

 le rest endosperm cells, are developed. A pollen grain 

 jposited on the stigma, sends out a hypha-like prolongation, 

 le pollen tithe, which elongates, passes down the style, and 

 /entually reaches the micropyle of an ovule. Traversing 

 le micropyle, the end of the pollen tube penetrates the 

 ucleus, and comes into close contact with the embryo sac. 

 'his is the process of impregnation, and the result of it 

 1 that the embryo cell divides and gives rise to a cellular 

 <iibryo. This becomes a minute Bean-plant, consisting of a 

 xdicle or primary root ; of two, relatively large, primary 

 ;aves, the cotyledons; and of a short stem, the plumule, on 

 rhich rudimentary leaves soon appear. The cotyledons now 

 icrease in size, out of all proportion to the rest of the em- 

 ryonic plant ; and the cells of which they are composed be- 

 ome filled with starch and other nutritious matter. The 

 iucleus and coats of the ovule grow to accommodate the en- 

 irging embryo, but, at the same time, become merged into an 

 mvelope which constitutes the coat of the seed. The pistil 

 inlarges and becomes the pod ; this, when it has attained its 

 uU size, dries and readily bursts along its edges, or decays, 

 etting the seeds free. Each seed, when placed in proper con- 

 litions of warmth and moisture, then germinates. The cotyle- 

 lons of the contained embryo swell, burst the seed coat, and, 

 jecoming green, emerge as the fleshy seed leaves. The nutri- 

 ,ious matters which they contain are absorbed by the plumule 

 md radicle, the latter of which descends into the earth and 

 Decomes the root, while the former ascends and becomes the 

 item of the young bean-plant. The apex of the stem retains, 

 throughout life, the simply cellular structure which is, at 

 first, characteristic of the whole embryo; and the growth 

 n length of the stem, so far as it depends on the addition of 

 lew cells, takes place chiefly, if not exclusively, in this part. 



