336 GENEBAL BOTANY 



is thus composed of the seed coat, or integument (which forms 

 a part of the mother sporophyte plant), of the gametophyte, and 

 of the young sporophyte, or embryo, which represents a new 

 sporophyte generation (Fig. 199, c). 



Life history. The life history of the spruce is similar in all 

 essential respects to that of the cycads, represented by Zamia. 

 In both instances the megaspore is permanently retained in the 

 megasporangium. In the spruce and its relatives the male 

 gametes have lost their motile organs, and the pollen tube is 

 consequently used to convey them to the eggs. Correlated with 

 this change we find that the spruce has no archegonial chamber, 

 since the pollen tubes enter the archegonial necks and intro- 

 duce the male gametes directly to the eggs. The results of ferti- 

 lization are the development of the embryo and the formation 

 of a seed. In order to have these points of difference between 

 the cycads and the spruce clearly in mind the student should 

 construct a graphical history of the spruce similar to that of 

 Zamia (Fig. 18.9> 



