THE GYMNOSPERMAE : CYCADALES, ETC. 



763 



result. The use of undefined terms such as " perianth," " ovary " and 

 " cupule " really explains nothing. The principal fact is that they arise in 

 acropetal succession as outgrowths of the base of the ovule itself and so 

 cannot be regarded as modified bracts subtending the ovule. Both appear 

 to arise from paired primordia, decussately placed, which fuse together at a 

 very early stage. One or perhaps both may be equated to the paired perianth 



e 



e 



B 



Ephedra 



e 



© 



B 



Gnetum 



Fig. 763 — Comparison of the floral diagrams of Ephedra 

 and Gnetum. A, Male flowers. B, Female flowers. 

 {After Eichler.) 



scales of the male flower, both here and in Ephedra, but the complete inter- 

 pretation of the ovular coverings, not only in Gnetales but throughout the 

 Gymnosperms, is not yet known. 



The outer covering is fleshy, the middle covering is sclerotic but has a 

 thick parenchymatous mantle round its upper end. The inner covering is 

 prolonged into a long tubular beak, which projects through the micropyle 

 beyond the outer coverings. This tube has two whorls of hairs, one directed 

 upwards and another, lower down, directed downwards and engaging with 

 the apex of the middle covering. The proliferation of the lining cells of the 

 tube occludes its internal passage, and subsequent growth of the middle 

 covering breaks the tube at the level of the lower whorl and lifts it clear of 

 its basal portion, where it remains in the mature seed as a stopper, closing 

 the micropyle. 



