GYMNOSPERMS 437 



understood. Ovules were thought to be little eggs; that 

 is what the word ovule means. Of course we know now 

 that the ovule, even though it contains the egg, does not 

 belong to the same generation as the egg. In spite of such 

 inconsistencies, this and the other old terms which describe 

 the parts of flowers will continue to be used. They are 

 convenient, and there is certainly no harm in using them 

 as long as they are understood. 



G. Pollen Grains not Exactly Microspores. — It is not 

 altogether accurate to call pollen grains microspores. In 

 a young pollen sac which has not yet opened you can find 

 pollen grains which are microspores; that is, they are 

 single cells. But when pollen grains are shed, they have 

 ceased to be single cells. They contain a number of nuclei, 

 and so, strictly speaking, they have ceased to be micro- 

 spores. They now contain the diminutive male game- 

 tophytes. There are two sperm cells. These and a so-called 

 tube cell migrate down the pollen tube. They constitute 

 practically all that there is to the male gametophyte. 



H. The Female Gametophyte. — ■ In gymnosperms this 

 generation is composed of very many more cells than is 

 the male gametophyte. (See Figure 226) Only one female 

 gametophyte is developed in each ovule. It comes to 

 occupy most of the interior of the ovule. It keeps on 

 growing after fertilization and forms that tissue known as 

 endosperm. The endosperm furnishes nourishment to the 

 embryo, especially when the seed begins to sprout. (See 

 Figure 227.) 



I. Generations in the Seed. — How many generations 

 are represented in the seed ? The hard outer coat known as 



