MORPHOLOG Y. 



group, that the sperm cells are well-formed spermatozoids. In zamia each 

 one is shaped somewhat like the half of a biconvex lens, and around the con- 

 vex stirface are several coils of cilia. After the 

 pollen tube has grown down through the nucel- 

 lus, and has reached a depression at the end of 

 the prothallium (endosperm) where the arche- 

 gonia are formed, the spermatozoids are set 

 free from the pollen tube, swim around in a 

 liquid in- this depression, and later fuse with 

 the egg. In gingko and cycas these spermato- 

 zoids were first discovered by Ikeno and Hirase 

 in Japan, and later in zamia by Webber in this 

 country. In figs. 371-374 the details of the 

 male prothallia and of fertilization are shown. 



634. The sporophyte in the gymnosperms. 

 In the pollen grains of the gymnosperms we 

 easily recognize the characters belonging to the 

 spores in the ferns and their allies, as well as in 

 the liverworts and mosses. They belong to the 

 same series of organs, are borne on the same 

 phase or generation of the plant, and are practi- 

 cally formed in the same general way, the 

 variations between the different groups not being greater than those within 

 a single group. These spores we have recognized as being the product of 

 the sporophyte. We are able then to identify the sporophyte as that phase 

 or generation of the plant formed from the fer- 

 tilized egg and bearing ultimately the spores. 

 We see from this that ihe sporophyte in the 

 gymnosperms is the prominent part of the 

 plant, just as we found it to be in the ferns. 

 The pine tree, then, as well as the gingko, cycas, 

 yew, hemlock-spruce, black spruce, "the giant 

 redwood of California, etc., are sporophytes. 



While the sporangia (anther sacs) of the male 

 flowers open and permit the spores (pollen) to be scattered, the sporangia of 

 the female flowers of the gymnosperms rarely open. The macrospore is de- 

 veloped within sporangium (nuccllus) to form the female prothallium (en- 

 dosperm). 



635. The gametophyte has become dependent on the sporophyte. In this 

 respect the gymnosperms differ widely from the pteridophytes, though we see 

 suggestions of this condition of things in Isoetes and Selaginella, where the fe- 

 male prothallium is developed within the macrospore, and even in Selaginella 

 begins, and nearly completes, its development while still in the sporangium. 



Fig. 372. 



Fertilization in cycas, 

 small spermatozoid fusing 

 with the larger female nu- 

 cleus of the egg. The egg 

 protoplasm fills the archego- 

 niutn. (From drawings by 

 Hirase and Ikeno.) 





a tail. (After Ikeno and 



