448 



FOURTH GROUP. SEED-PLANTS. 



upper and usually the larger part of the fusiform body consists of the hypocotyledonary 

 portion of the stem (hypocotyt], and it is only the lower, posterior, often very short 

 terminal piece which is the rudiment of the primary root (Fig. 377); in the tissue of 

 this latter the first rudiments of the secondary roots may sometimes be distinguished, 

 as in Cucurbita, and according to Reinke in Impatiens. 



FIG. 377. Phaseolus muttiflorus. Longitu- 

 dinal section of the axis of the embryo in the ripe 

 seed parallel to the cotyledons ; ss apex of the stem, 

 ws apex of the root, he hypocotyl, ct cushions at the 

 point of insertion of the cotyledons, i the first 

 internode, /* the stalks of the first foliage-leaves, 

 v vf rudiments of the vascular bundles. Magn. 

 about 30 times. FIG. 378. Ricinus communis. Young plant ; w the primary root, n secondary 



roots, h hypocotyl, c cotyledons. 



Germination. After the seed-coat or, in dry indehiscent fruits, the pericarp has 

 been ruptured by the swelling of the endosperm or the cotyledons, germination 

 usually begins with the elongation of the hypocotyl and the consequent protrusion of 

 the root from the seed ; the root then begins to grow rapidly, and usually reaches a 

 considerable length and forms secondary roots in acropetal succession, while the 

 cotyledons and the plumule remain still in the seed (Figs. 375, 376, 377, 378). 



