462 THE BEAN PLANT. [CHAP. 



The cotyledons of the contained embryo swell, burst the 

 seed coat, and, becoming green, emerge as the fleshy seed 

 leaves. The nutritious matters which they contain are ab- 

 sorbed by the plumule and radicle, the latter of which de- 

 scends into the earth and becomes the root, while the former 

 ascends and becomes the stem 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 in length of the stem, so far as it 

 depends on the addition of new cells, takes place chiefly, if 

 not exclusively, in this part. The growing point does not 

 terminate in a single apical cell, as in the Fern, but con- 

 sists of a number of small, actively dividing cells, termed 

 collectively the apical meristejfi. The root likewise develops 

 its tissues from an apical meristem, but this, as in the Fern, 

 is protected by a root-cap. 



The leaves cease to grow by cell multiplication at their 

 apices, when these are once formed, the addition of new 

 cells taking place at their bases. Each leaf is compound, 

 the common petiole bearing from four to six leaflets. 



The tissues which compose the body of the Bean-plant 

 are similar, in their general characters, to those found in the 

 Fern, but they diff"er in the manner of their arrangement. 

 The surface is bounded by a layer of epidermal cells, among 

 which are stomata similar to those described in the Fern. 

 Within the epidermis is a broad zone of tissue, termed 

 the cortex. The greater part of this zone consists of paren- 

 chymatous cells of the usual structure. At the four pro- 

 jecting corners of the stem however, the cortical tissue 

 has a somewhat different structure, consisting of cells which 

 have their walls much thickened at the points of junction. 

 Within the cortex comes a ring of vascular bimdles, and 

 within this is the parenchymatous///// extending to the very 



