SEED-BEARING PLANTS 



437 



called the style. Through the center of the style extends 

 a tiny canal, so that the style is hollow. The walls of this 

 canal, in Erythronium, are lined with a glandular layer of 

 cells forming the conducting tissue, which serves to nourish 

 the pollen- tubes (Fig. 324). An expansion of this tissue is 

 exposed at the tip of the style, forming the stigma, or surface 

 for the reception of the pollen-grains in pollination. The 

 conducting tissue extends continuously from the stigma 

 down through the style to the placenta, or point of attach- 

 ment of the ovules. 



FIG. 324. Erythronium americanum. i, longitudinal section of hollow 

 style, showing glandular cells of the conducting tissue lining the canal; 

 2, microspore; 3, young pollen grain (male gametophyte), showing gen- 

 erative nucleus and tube nucleus; 4, pollen-grain germinating, i and 4 

 are from E. albidum. (After J. H. Schaffner.) 



In many plants the style is not hollow, and the con- 

 ducting tissue completely fills the center. The stig- 

 matic surface secretes a sticky substance by which the 

 pollen-grains are held fast. In some species of plants 

 this surface is covered with tiny hairs, by which the 

 pollen-grains are held until they germinate. 



390. Pollination. The flower of Erythronium stands 

 out in sharp contrast to that of the gymnosperms, in two 

 respects, namely, the occurrence of both stamens and 

 carpels in the same flower, and the possession of a con- 

 spicuous, colored perianth. The significance of the 



