GXETALES 



125 



'he nucleus of the spore begins free nuclear division, the nuclei 

 become imbedded in a parietal layer of cytoplasm which sur- 

 rounds a great central vacuole, and free nuclear division con- 

 tinues until numerous nuclei appear within the enlarging em- 

 bryo sac. Walls next appear, and a layer of parietal tissue 

 develops, which by continued cell division gradually fills the 

 sac with a compact tissue, as in Conifers. The archegonia have 

 unusually long necks, and apparently a remarkably persistent 

 ventral canal cell. 



It is evident that in Ephedra there is the least departure 

 from what may be called the Gymnosperm type of female 

 gametophyte, and presumably Ephedra may be regarded as the 

 most primitive of the Gnetales. 



Tumboa. This genus needs re investigation from the stand- 

 point of modern technique and modern morphology, for the 

 facts recorded concerning it are somewhat vague and may be 

 misleading. Xothing is known of the development of the soli- 

 tary functional megaspore further than that it lies at first deep 

 within the nucellus beneath long rows of wall cells. As this is 

 true of Gymnosperms in general, it may be assumed that the 

 history up to this point is the same. 



Apparently the germination of the megaspore also proceeds 

 in the usual way, with free nuclear division, imbedding of the 

 free nuclei in a parietal layer of cytoplasm, appearance of walls, 

 and gradual centripetal filling of the embryo sac. It is evident, 

 however, that the tissue in the micropylar end of the embryo 

 sac is less compacted than that in the antipodal end. In any 

 event, the archegonium initials upon the micropylar surface of 

 the gametophyte behave in an exceedingly peculiar and inde- 

 pendent fashion. It is reported that there are from twenty to 

 sixty of these initials, and that they proceed no further in the 

 development of archegonia than to assume the appearance of 

 ordinary archegonium initials, an egg being organized directly 

 within each of them without any division. Just why the devel- 

 opment of archegonia should stop with the selection and en- 

 largement of initial cells is hard to understand except upon the 

 hypothesis that they are practically free cells. Each of these 

 cells, representing a greatly reduced archegonium, contains an 

 gg which is ready for fertilization. There is suggested an inter- 

 mediate condition between Epliedra, with its complete arche- 



