284 



PLANT LIFE. 



to traverse the pistil. Pollen tubes may, therefore, grow 

 10-15 cm. in length. Usually the older part of the tube dies 



Fig. 321. 



Fig. 322. 



Fig. 320. — Anterior fourth of female gametophyte of spruce (Pz'cea excelsa), showing 

 two ovaries, e, tissue of gametophyte (endosperm); a, egg; k. nucleus of egg; h, 

 neck of ovary (the line does not reach the neck, which is situated in a depression of the 

 plant below h ; the shading shows the side of this slope); kz, neck canal cell. See fig. 

 321. Magnified 50 diam. — After Strasburger. 



Fig. 321. — A. portion of the ovary of the spruce, seen as in fig. 320, but magnified 165 

 diam. The cell kz of fig. 320 has become disorganized to make way for the pollen 

 tube, fi, which has pushed between the neck cells and reached the egg, e, into which 

 one of the sperms in its tip is about to enter, g, tissue of the female gametophyte. — 

 After Strasburger. 



Fig. 322. -Upper part of ovule of red cedar, with integument removed, nu, mega- 

 sporangium ; at, female gametophyte with three ovaries of a cluster of six ; /, pollen 

 tube. Each ovary shows an elongated egg and above the small neck cells. The left- 

 hand pollen tube has two sperms about to pass between neck cells into an egg. Magni- 

 fied 67 diam.— After Strasburger. 



as the tip advances. The food needed is chiefly derived 

 from the cells of the stigma and style which it disorganizes. 



