28 MORPHOLOGY OF SPERMATOPHYTES 



It is helpful to contrast the spermatogenous series in Cycads, 

 which is the same as in other Gymnosperms, with that in such 

 a Pteridophyte as Isoetes. The sequence may be expressed 

 diagrammatically (Fig. 24), the terminology of the Gymno- 

 sperms being used. 



At one time it seemed to us desirable to homologize this 

 series, if possible, with spermatogenesis as observed in animals, 



and to use the same 

 terminology. Up- 

 on further inves- 

 tigation, however, 

 we have concluded 

 that such an at- 

 Sperms tempt is at present 



FIG. 24. Diagram contrasting spermatogenesis in Cycads impossible In ani- 

 and Isoetes. 



mals there is no de- 

 nned alternation of generations, and in their spermatogenesis 

 the reduction division is an important feature, so that merely 

 matching generation with generation in the spermatogenesis of 

 the two series would probably be very far from indicating any 

 true homologies. 



It should be said that ciliated male cells have been actually 

 observed as yet in but three species of Cycads : in Cycas revoluta 

 by Ikeno, in Zamia integrifolia by Webber, and in Stangeria 

 paradoxa by Lang. 



FERTILIZATION 



Immediately after the male cells have become transformed 

 into ciliated sperms, the events intimately connected with fer- 

 tilization begin to occur. The more or less extensive pollen 

 tube system, which has been penetrating the loose nucellar 

 tissue capping the embryo sac, is abandoned, the tissue becomes 

 disorganized and collapses, and the gametophyte structures 

 within the pollen chamber are brought sensibly nearer the em- 

 bryo sac. The pollen tube region in connection with the pollen 

 grain then begins to develop, and this end of the tube, contain- 

 ing the tube nucleus and sperms, is turned toward the embryo 

 sac, its end capped by the old microspore wall (Fig. 18). Upon 

 reaching the wall of the embryo sac overlying the archegonial 

 chamber resorption of walls probably occurs, but in any event the 



