430 MORPHOLOGY OF GYMNOSPERMS 



individual roots, the first-formed portion being tetrarch and the tip 

 diarch. In Ginkgo the diarch root is the one commonly found, 

 though here also tetrarchy and triarchy sometimes occur. The root 

 of Gnetales is diarch. 



"At this point, also, comparison with the angiosperms is instructive. 

 Both tetrarch and diarch roots occur among the Archichlamydeae. 

 According to Miss Thomas, the anatomy of the cotyledonary node 

 of Liriodendron tulipifera, Clematis Hendersonii, species of Quercus, 

 of Ricinus, and even some Compositae, resembles in every respect 

 that of Cycas and Dioon. 



"A third tendency made apparent by this comparison of seedling 

 anatomy is that to reduce the cotyledonary vascular strands to the 

 fixed number two. The Coniferales are the only order to work out 

 this tendency to the end; the dicotyledonous conifers (except Araii- 

 caria and Podocarpus) have just two such strands, one for each 

 cotyledon. The Cycadales, although they have not reached that 

 condition, show a tendency toward it in two ways: by restricting the 

 branching of both median and lateral strands, and by eliminating 

 the lateral ones altogether; and both of these tendencies are carried 

 into the angiosperms. The cotyledon in Ginkgo and the Gnetales 

 receives two strands, which often dichotomize. 



" Two very interesting facts are brought out by the diagram in the 

 third row of fig. 462 (series C) . One of these is the strong resemblance 

 between Ginkgo and the Gnetales; the other is the disclosure that in 

 this feature of seedling anatomy, as well as in many other respects, 

 Araucaria and Podocarpus stand aloof from the other conifers and 

 show a marked resemblance to Ginkgo. These two facts may or 

 may not be significant; the series was constructed merely to show 

 that they exist." 



