GROUPS OF PLANTS. 



89 



forest trees. After the deposition of the pohen grain on the stigma, 

 the tube-cell begins to form a tubular process (pollen tube) which 

 carries the male nuclei to the egg-cell (Fig. 85, i). It pierces 

 the tissue of the stigma (Fig. 85, h) and traverses the style (Fig. 



jj4Q\0SPERMS 



unicelIlular 

 fuagIellatE 

 greenIalga^ 



Fig. 58. Hypothetical tree of relationship and descent of the leading groups of plants. 



After Ganong. 



85, g) until it reaches the micropyle of the ovule, which it enters 

 (Fig. 85, m), then reaching the nucellus it penetrates this, enter- 

 ing the embryo-sac. The tip of the tube breaks and one of the 

 generative nuclei which has been carried downward unites with the 

 egg, after which a wall is formed, giving rise to an oospore. The 



