^-GNETALES 371 



compound ovulate strobili occur among Cordaitalcs and Conifcrales, 

 com])ound staminate strobili are restricted to Gnetales. If the 

 strobilifcrous shoot of Torreya taxijolia, with its simple axillary 

 strobili, were compacted into a strobilus, the condition among Gne- 

 tales would be attained. To avoid confusion we will call these simple 

 axillary strobili of Gnetales flowers, to distinguish them from the 

 compound strobilus which they make up. It must be remembered, 

 however, that they are flowers only in the sense that the simple strobili 

 of Taxus and Torreya are flowers. The whole group is prexailingly 

 dioecious. 



THE MICROSPORANGIUM 



In Ephedra the flowers are monosporangiate and generally dioe- 

 cious, arising from the axils of broad imbricate bracts, which in decus- 

 sating pairs form a short, membranaceous strobilus (fig. 414). These 

 strobili occur in pairs at the nodes, one arising from the axil of each 

 of the opposite and minute scalelike leaves. Occasionally an ovulate 

 flower replaces a staminate one (18), so that the strobilus, but not the 

 flower, becomes bisporangiate. 



The staminate flower consists of two more or less connate scales 

 ("perianth") investing a projecting axis that bears two or more 

 sporangia. This stamen, which is evidently an axial structure, 

 may remain simple, in which case it bears two sporangia; or it may 

 branch somewhat above and bear several sporangia. The period of 

 development is remarkably short, the staminate strobilus of E. tri- 

 jurca first becoming evident in December (in New Mexico), the 

 mother cells in Februarv, the reduction divisions in March, and 

 pollination in April. A " resting period " of one month for the mother 

 cell is a remarkably short one for a gymnosperm. The anthers mature 

 in acropetal succession in the strobilus, and the only account of the 

 development of the microsporangium of Gnetales is that of Land 

 for Ephedra trijurca (18). In the organogeny of the flower the stamen 

 appears first, and the "perianth" later, but before there is any differ- 

 entiation of an archesporium. Apparently the archesporium is a 

 single hypodermal cell (in transverse section), dividing periclinally 

 as usual. The primary wall layer divides periclinally, but there are 

 no further periclinal divisions, so that there is only a single layer 



