6^6 



PHANEROGAMS, 



between them is pushed out (Fig. 438), 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. 

 In order to liberate them and the plumule which lies between them from the seed, 

 the hypocotyledonary portion of the axis increases considerably in length, making 



Fig. 437. — Longitudinal section of the axis of the 

 embryo in the ripe seed of Phaseolus fniMiflorus , 

 parallel to the cotyledons {X about 30) ; ss apex of the 

 stem, ws of the root, ct cushion at the insertion of 

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

 the first foliage leaves, v,v,f\}s\& procambium of the 

 fibro-vascular bundles. 



Fig. 438. — Qiiercus Robiir ; I longitudinal section of the embryo (mag- 

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

 hypocotyledonary portion of the axis he, the primary root iu, 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 sh and pericarp s by the elongation of the petiole of the cotyledons 

 st, w primary root, iu' secondary roots. 



first of all a curve which is convex on the upper side (Fig. 435), because the coty- 

 ledons still remain in the seed while the lower end of the stem is attached by the 

 root to the ground. Ultimately, by a final lengthening of the hypocotyledonary 

 portion, the upper part of the axis together with the cotyledons is drawn out of 

 the seed in a pendent position. The axis now straightens as it continues to grow, 

 and the cotyledons expand in the air, the plumule developing more completely and 



