28 GYMNOSPERMS 



PHYLOGENY 



What was the origin of the group? From their striking resem- 

 blance to ferns it was natural to assume that they were modified 

 ferns, and the English promptly named them "Seed Ferns," or, to 

 say it in Greek, "Pteridosperms." The earlier name, Cycadofilices, 

 based upon the anatomy of the stem, was discarded. While the name 

 "Seed Ferns" is appropriate, the plants are true gymnosperms, as we 

 have said before, and not separated from them by any character of 

 such importance as separates the gymnosperms from the angio- 

 sperms. So we simply use the earlier term, modifying the ending to 

 indicate its ordinal rank. 



Gradually, our English friends became skeptical about any fern 

 origin of the group. The argument that, historically, the Cycadofili- 

 cales have been found as far back as the FiUcales has practically no 

 weight; for the evidence is not all in yet. The claim that vascular 

 anatomy is against derivation from ferns is not convincing; for the 

 advance in stelar development is about what one should expect. The 

 dominant sclariform tracheid of the ferns has given way largely to 

 the pitted tracheid. The fact that secondary wood is so prevalent in 

 the Cycadofilicales is not surprising. It is an advance in stelar de- 

 velopment, but it does not separate ferns from seed ferns; for even 

 some living Pteridophytes of rather insignificant size, like Bolrychi- 

 um, have secondary wood; and the pitting stage has been reached, 

 even by some of the living homosporous Pteridophytes. On the other 

 hand, a seed plant may retain the fern sclariform tracheid, even in 

 the secondary wood, as in Siangcria. 



We believe that the leaf affords strong evidence of a derivation 

 from ferns. The reproductive structures reached the seed level while 

 the leaves were little or not at all modified. This would make it very 

 natural to mistake the leaves of these early seed plants for those of 

 ferns. Of course, everyone knows that plants entirely unrelated to 

 each other may have very similar forms. Euphorbia canaricnsis looks 

 like a cactus in the organ cactus group, but the superficial resem- 

 blance does not make any trouble for the taxonomist. Many of the 

 Euphorbiaceae look like cacti. Slapclia, one of the Asclepiadaceae, 

 also looks like a cactus. Equisetum, Ephedra, and some species of 

 Casuarina are strikingly similar in some features, although so widely 



