510 



PART IV. CLASSIFICATION. 



dium, the uppermost lateral bud growing each year in the direction 

 of the main axis, which does not itself develop any further (p. 21). 

 When the axis of the embryo continues to be the main axis of 

 the plant, the primary root also develops greatly, and forms a 

 tap-root from which the lateral roots grow in acropetal succession. 

 In cases in which the growth in length of the tap-root is limited, 

 numerous adventitious roots spring from its older portions ; these 

 may again give rise to lateral roots, and by a repetition of this 

 process an elaborate root-system is formed. 



FIG. 32 1 . Ftrta Faba, the Bean. A Seed with one of 

 the cotyledons removed ; c the remaining cotyledon ; 

 IT radicle ; fcn plumule ; s testa. B Germinating seed ; 

 s testa ; I a portion of the testa torn away ; n hilum ; 

 st petiole of one of the cotyledons; fc curved epi- 

 cotyl ; he the very short hypocotyl ; h the primary 

 root; twits apex; fcn bud in the axil of one of the 

 cotyledon*. 



FIG. 321. Seedling of the Maple 

 (nat. size): c c the cotyledons; fc 

 the plumule; he the hypocotyl; 

 11- primary root; h root hairs 

 (the lower part is cut off). 



The stem is almost always monostelic (see p. 117). The vas- 

 cular bundles of the stem are almost always conjoint, collateral. 

 and open, and the stem grows in thickness by the activity of the 

 cambium -ring which is formed (p. 137). When the stem grows in 

 thickness, the root does so also. 



