SPERMATOPHYTES : GYMNOSPERMS 



187 



This " awakening " of the seed is spoken of as its " ger- 

 mination/' but this must not be confused with the germi- 

 nation of a spore, which is real germination. In the case 

 of the seed an oospore has germinated and formed an embryo, 

 which stops growing for a time, and then resumes it. This 

 resumption of growth is not germination, but is what 



FIG. 157. Tip of pollen tube of Cycas revoluta, containing the two spiral, multiciliate 

 sperms. After IKENO 



happens when a seed is said to "germinate." This second 

 period of development is known as the extra-seminal, for it 

 is inaugurated by the escape of the sporophyte from the 

 seed (Fig. 154). 



104. The great groups of Gymnosperms. There are at 

 least four living groups of Gymnosperms, and two or three 



