DICOTYLEDONS. 



559 



selves — by the elongalion of the hypocotyledonary portion of the axis to such an 

 extent as to push the radicle out of the seed, the root then beginning to grow 

 rapidly and generally attaining a considerable length and forming secondary roots 

 in acropetal succession, while the cotyledons and plumule still remain in the seed 

 (Figs. 404, 405, 406). Thick fleshy cotyledons usually remain in the seed during 

 germination, finally perishing after their food-material has been consumed (as in 



Fig. 406.— Longitudinal section of the axis of the 

 embryo m the ripe seed of Phaseolus miiltiflorus, 

 parallel to the cotj'lcdons (X about 30), jj apex of the 

 stem. 7US of the root, ct cushion at the insertion of the 

 cotyledons, zthe first internode,/A the petioles of the 

 first foliage-leaves, -v, v, f the procambium of the 

 fibro-vascular bundles. 



Fig. 407. — Querciis Rohur : /longitudinal section of the embrj-o (mag- 

 nified) after removal of the anterior half of both cotyledons c, c; the 

 hypocotyledonary portion of the axis he the primary root iv and plumule 

 b are concealed between the lower portion of the thick cotyledons ; st 

 petiole of the cotyledons ; // seed at the time when germination is com- 

 mencing (natural size), the pericarp and one cotyledon have been removed, 

 the hypocotyledonary portion of the axis and the radicle have elongated ; 

 /// further stage of germination, the plumule having emerged from the 

 testa sk and pericarp s by the elongation of the petiole of the cotyledons 

 st, IV primary root, 2v' secondary roots. 



Phaseolus mul/iflorus, Vkia Faba, Fig. 405, Quercus, Fig. 407). In this case the 

 petioles of the cotyledons lengthen so much that the plumule which is concealed 

 between them is pushed out (Fig. 407), and now grows upright so that the seed 

 and cotyledons together have the appearance of being a lateral appendage of the 

 axis of the embryo. But usually the cotyledons are destined for further develop- 

 ment, especially when they are thin, and form the first foliage-leaves of the plant. 



