ANGIOSPERMS 



385 



for the seedling at time of germination. This is called the peri- 

 sperm. The endosperm of the Angiosperms is not developed 

 unless fertilization takes place, even in those cases where double 

 fertilization may not occur. 



549. In case of crosses between different varieties of plants, the 

 effect of the cross usually is not apparent in the seed because the 

 qualities of the two parents are united in the embryo and would 

 not be shown until the embryo develops into a plant, or in a fol- 

 lowing generation. Sometimes, however, the effect of the cross 

 is seen in the seed formed following fertilization, as for example 



Fig. 382. 



Seed of violet, external view, and 

 section. The section shows the embryo 

 lying in the endosperm. 



Fig. 383- 



Section of fruit of pepper (Piper 

 nigrum), showing small embryo lying 

 in a small quantity of whitish endo- 

 sperm at one end, the perisperm 

 occupying the larger part of the in- 

 terior, surrounded by pericarp. 



In corn, where there is a change in color of the seed when differ- 

 ent colored varieties are crossed. This phenomenon is called 

 xenia and is perhaps the result of double fertilization, the fusion 

 of the second sperm nucleus with the two polar nuclei to form 

 the primary endosperm nucleus which forms a hybrid endosperm. 

 550. The embryo and seed. The fertilized egg cell which is 

 near the micropylar end of the embryo sac, now by a series of 

 divisions, and by growth, forms the embryo. At first it forms a 

 simple cell mass with a suspensor at one end, which pushes the 

 growing point down into the mass of endosperm. Soon the parts 

 of the embryo (root, stem and leaf bud) are organized and the 

 seed ripens. In some plants only a small part of the endosperm 

 is used by the embryo before the seed ripens,, as in the corn, cereals, 

 etc. (albuminous seeds) ; in others the endosperm is all consumed 



