THE GYMNOSPERMAE : CYCADALES, ETC. 755 



]\Iost probably it varies, being partly of one nature or the other in different 

 species. Each anther is supplied with one vascular bundle, derived from 

 the branching of the pair of bundles which enter the stalk at its base, the 

 branches running parallel upwards to the anthers. 



The anthers themselves have either two or three lobes, each lobe opening 

 by an apical slit. The pollen grains are elliptical. 



The Female Strobilus. 



The female strobili are distributed in the axils of the leaves on the young 

 shoots in the same way as the males, and they are very similar in structure 

 though rather shorter, with only two to four pairs of 

 bracts (Fig. 757). Each strobilus ends in a group of 

 female flowers, one, two or three in number, each 

 consisting of a nucellus with two envelopes. The 

 arrangement recalls that in the Taxales, and a similar 

 difficulty of morphological interpretation meets us 

 here. The inner envelope is formed of two segments 

 and contains two bundles, while the outer envelope 

 is formed of four segments and has four bundles. 

 Comparison with the flowers of Welwitschia suggests 

 that the nucellus is terminal on a suppressed 

 branchlet of the strobilus, that the inner envelope 

 is a true ovular integument, and that the outer 

 envelope is a perianth, the whole structure being 

 axillar}' to one of the bracts of the uppermost 

 pair. 



The upper half of the nucellus is free from the 

 inner integument, and the latter is prolonged into a 

 thin-walled micropylar tube which is sometimes 

 spirally twisted and opens at its tip into a tongue- 

 like extension. Here the pollination drop is extruded, 

 by means of which pollen is drawn down into the 

 micropylar tube. The perianth fits closely over the 



integument and becomes woody or fleshy, forming the outer coat of the 

 developed seed. 



The bracts of the strobilus are in some species dry and winged, in others 

 fleshy and sometimes brightly coloured, corresponding to the means of 

 dispersal, either by wind or by animals, which is characteristic of the particular 

 species. 



Fig. 757. — Ephedra ititer- 

 juedia. Female stro- 

 bilus with two female 

 flowers. {After Stapf.) 



The Male G.^metophyte. 



The divisions of the nuclei in the microspore follow the Piniis plan, a 

 small but positive sign of linkage with the Conifers. Two prothallial cells 

 are formed, together with an antheridial stalk cell and a body cell, the latter 



