OYCADALBS 



11 



or they may occur in definite groiips of two to five, wliicli may 

 be called sori, as in Cycas, Stangeria, and Zamia (Fig. 9). 



The first full account of the development of the microspo- 

 rangium was published by Treub ^■^ in 1881, who investigated 

 especially Zamia muricata. The latest investigation is that of 

 Stangeria paradoxa by Lang,^^ who has confirmed Treub's re- 

 sults in a general way, and has 

 cleared up certain points which were 

 doubtful. 



The first indication of a sporan- 

 gium is the differentiation of a 

 hypodermal plate of cells (four in 

 Stangeria), which constitutes the 

 archesporium (Fig. 10). This arche- 

 sporium has been homologized with 

 the hypodermal plate of cells which 

 appears in the development of the 

 microsporangia of heterosporous 

 Pteridophytes. It should be remem- 

 bered, however, that the periblem 

 always gives rise to the archespori- 

 um, and that this region, in the ab- 

 sence of a dermatogen, is superfi- 

 cial in the Pteridophytes. It would 

 seem to follow, therefore, that a 

 true homology would regard the 

 archesporium as superficial in Pteri- 

 dophytes and hypodermal in Sper- 

 matophytes. In presenting Treub's 

 results for Zamia, in which the 

 archesporium is spoken of as a hypo- 

 dermal group of cells, GoebeP'^ re- 

 marks that " there is without doubt a unicellular archesporium." 

 In Stangeria, however, Lang was unable to trace the plate of four 

 cells to a single one, and a one-celled archesporium for the micro- 

 sporangia of Cycads still remains to be proved. Each cell of 

 the archesporial plate divides by a periclinal wall into a tabular 

 outer and a larger inner cell (Fig. 10). The outer daughter 

 plate is sterile, and there is no evidence that it contributes to 

 the sporogenous tissue, as in some Pteridophytes. It is com- 



FiG. 8. — Zamiamwricata: A, stam- 

 inate strobilus, two thirds nat- 

 ural size ; B, transverse section 

 of ^ ; C, single peltate stamen 

 showing attachment of spo- 

 rangia ; i), upper part of ovu- 

 late strobilus, two thirds natu- 

 ral size ; E, transverse section 

 of D ; F, longitudinal section 

 of a ripe seed. — After Kar- 



STEK. 



