SEED PLANTS 169 



microspore produces a rudimentary antheridium with 

 two sperm-cells, much as in Cycas, but so far as known 

 at present, the formation of spermatozoids is completely 

 suppressed. It would not be surprising, however, if 

 some trace of such structures should be discovered. 

 The germination of the pollen-spore when it falls upon 

 the ovule is like that of Cycas, but the pollen-tube pene- 

 trates through the neck of the archegonium, and the 

 sperm-nucleus is discharged directly into the egg. 



In the higher Conifers, such as the pines and firs, the 

 macrosporangia are developed upon special sporophylls 

 (carpels) which not infrequently are borne in the axils 

 of sterile bracts. The sporophylls are arranged spirally 

 about the axis of a shoot, forming the familiar " cones " 

 of these trees. As in the yew, the single macrospore 

 which is finally formed in the sporangium produces 

 the large female gametophyte, much like that of Sela- 

 ginella. The archegonia are several in number, with 

 very large egg-cells, but the neck parts relatively small, 

 as they are in all Gymnosperms. The sporangium is 

 invested with a single integument as in the other forms 

 described. 



The microsporangia are also borne upon special sporo- 

 phylls, and are usually arranged in a cone like those 

 bearing the ovules. These microsporangia or pollen- 

 sacs correspond in every detail of their development 

 with those of the Pteridophytes. The ripe pollen- 

 spores in the pines (Fig, 42, E) and firs are provided 

 with wing-like outgrowths of the outer membrane, 

 which form very efficient sails by which they are more 

 easily scattered by the wind. As the pollen must de- 

 pend upon the wind for its distribution, the number of 



