ANGIOSPERJVLE 



357 



pollination takes place, the pollen of one flower being carried to the 

 stigma of another, either by the wind or by insects. 



The germination of the pollen-spore is stimulated by the secretion 

 usually developed from the stigmatic surface, and may be induced 

 artificially by placing the pollen in a solution of sugar. The pollen- 

 'tube is sometimes emitted within a few minutes, and its growth is 

 often extremely rapid. Either before or after germination has begun 

 the generative nucleus divides into two, and these are carried into the 

 developing tube, probably by the movements of the cytoplasm, which 

 are very active in the growing pollen-tube. The latter grows rapidly 



FIG. 322. Sparganium simplex. A, section of chalazal end of embryo-sac, showing 

 two of the antipodal cells and the endosperm nucleus, n. B, longitudinal section 

 of the developing endosperm (X 200). C, first cell-formation in the endosperm, 

 surface view (x 800). D, two sections of the antipodal cells after fertilization of 

 the egg (X400). 



through the style, where there is developed a special " conducting tis- 

 sue," whose cells contribute the material necessary from the growth 

 of the pollen-tube, which grows precisely like the hypha of a Fungus 

 through the tissues of its host. The conducting tissue is continued 

 into the placenta, or tissue to which the ovules are attached, and 

 along this the pollen-tube advances until it reaches the taaicropyle of 

 the ovule, into which it penetrates, and pushes through the tissue at 

 the apex of the nucellus and enters the embryo-sac. In most instances 

 it grows through one of the synergids, which is destroyed, and dis- 

 charges one of the generative nuclei into the egg, where it fuses 



