CYCADALES 



117 



young staminate cones of Zamia floridana and Chamberlain (63) 

 described spermatogenesis in Dioon edule. 



The sporophylls first appear as minute papillae, giving the young 

 cone a wavy contour as seen in longitudinal sections (figs. 96, 97). 

 According to Miss Smith, there is in Zamia a single archesporial cell, 

 the first division of which may be either periclinal or anticlinal, but 

 in any case primary wall cells and primary sporogenous cells are soon 

 formed (figs. 101-104). In Stangeria Lang (22) first recognized the 

 archesporium as a hypodermal plate of four cells (figs. 105-109). 

 By comparing these figures with those of Miss Smith, it is evident 



Fig. 100. — Microsporophylls of cycads : A, Cycas circinalis {a, entire sporophyll, 

 showing sporangia on under surface; 6, four groups of sporangia; c, same as 6 after 

 the pollen has been shed); B, Zamia integrifoUa (a, entire sporophyll; b, c, clusters of 

 sporangia). — Ab, Ac, after Bltjme; the rest after Richard; the whole figure taken 

 from Engler and Prantl's Natilrlichen Pflanzenfamilien. 



that Stangeria develops like Zamia, the hypodermal plate having 

 come from a single cell. The later stages are essentially the same in 

 both accounts. A sporangium wall several cells in thickness is 

 developed, and also a large mass of sporogenous tissue, from the 

 periphery of which the tapetum is differentiated. While the origin of 

 the tapetum was not studied in Dioon, fig. no would indicate that it is 

 more probably derived from the wall cells. The resemblance of the 

 cycadean sporangia to those of the marattiaceous fern Angiopteris 

 is quite striking, the principal difference being the comparatively 

 scanty development of the tapetum in the cycad (fig. in). As the 

 spores mature, the epidermal layer of the sporangium becomes thick- 



