144 Plant Life and Evolution 



The second genus of Gnetales, Ephedra, with 

 some twenty species, is represented in the United 

 States by two or three species of the arid Southwest. 

 In the Colorado desert, and the deserts of southern 

 Arizona, one frequently meets with these straggling 

 bushes, whose leafless, gray-green, jointed stems, re- 

 mind one of the horsetails. While these bushes are 

 very different in aspect from most conifers, the 

 structure of the seeds is quite similar, this being 

 especially the case with the highly developed 

 gametophyte. 



The third genus of the Gnetales, Welwitschia, has 

 but a single species, confined to a limited desert 

 region in Western Africa. This extraordinary plant 

 has a short, thick trunk, tapering into a long tap- 

 root, so that it looks like a great carrot or parsnip 

 with the top cut off. Growing from the margin of 

 the flattened trunk-apex are two immense strap- 

 shaped leaves, which are all the plant has. From 

 the margin of the trunk cones of flowers are also 

 produced. These are made up of large red scales, 

 which are very conspicuous, and, it is said, attract 

 insects so that the plant is sometimes, at least, cross- 

 pollinated. The more recent studies on this plant 

 by Professor Pearson, of Cape Town, indicate cer- 

 tain resemblances in structure to Gnetum, and it 

 is not impossible that the two genera are remotely 

 related. Ephedra probably is not related to either 

 of the other genera. Practically nothing is known 

 of the geological history of the Gnetales, but their 



