How Plants Perpetuate Their Kinds 



283 



seems by some chemical vapor exuded from the micropylar open- 

 ing of the ovule, grows straight thereto and enters, pursuing its 

 way until its tip comes to lie flat against the egg-cell. Then one 

 of the male nuclei moves out of the tube into the egg-cell (fig- 

 ure 100), and across it to the 

 nucleus thereof ; then the two 

 nuclei touch, flatten a bit 

 against one another, and 

 finally fuse and intermingle 

 completely. Thus the egg- 

 cell comes to possess a nucleus 

 made up from the two nuclei 

 derived from the two parents, 

 male and female; and this is 

 the central and most essen- 

 tial feature of fertilization. 

 The fertilized egg-cell is now 

 ready to grow into an em- 

 bryo, which, with certain ac- 

 cessory parts, forms the seed, 

 and later grows to an adult 

 new plant. 



I have described somewhat 

 fully this process of fertiliza- 

 tion as it occurs in an ordi- 

 nary plant because it is typi- 

 cal in principle of all fertilization through the plant and animal 

 kingdoms. The machinery varies immiensely of course in detail. 

 In some kinds of plants the sperm cell is not carried by a growing 

 tube, but, guided by certain attractive chemicals exuded by the 

 female parts, swims of itself in water to the egg-cell, as is the way 

 in Ferns, Mosses and many Seaweeds. In most animals, how- 

 ever, the male cells (called spermatozoids) are brought by suitable 

 organs to the near vicinity of the egg-cells, to which they finally 



Fig. 97. — A typical o\-ule (of Narcissus), seen in 

 optical longitudinal section, highly magnified. 

 The parts may be identified from the te.xt, 

 the most important being the egg-cell, which 

 is the larger of the three cells lying in the 

 upper end of the embryo sac. (Copied from 

 a wall-chart by Dodel-Port). 



