428 MORPHOLOGY OF GYMNOSPERMS 



varying amounts of endosperm-formation in different seeds, the great 

 diversity in thickness and induration of seed coats, the presence or 

 absence of the phenomenon of rest, the slowness or rapidity of ger- 

 mination. And the extremes of hypogeal and epigeal development 

 are found side by side in the oldest living gymnosperms. Ginkgo and 

 Pinus, with no historical evidence as to which is the more primitive 

 method. 



"Taking the facts as we find them, however, we cannot but be 

 impressed by the fairly harmonious testimony of certain evolutionary 

 tendencies manifested not only by the group as a whole, but by each 

 of the living orders. An inspection of the diagrams (fig. 462) will 

 help to make these tendencies apparent. The most obvious tendency, 

 perhaps, is that to reduce the cotyledons to the fixed number two. 

 Series A represents conditions as they are found among the Cycadales, 

 which, though younger than the Coniferales, are conceded to have 

 retained more primitive anatomical features. Though the order as 

 a whole is dicotyledonous, its more fernJike members are frequently 

 observed to be polycotyledonous; and cases of cotyledonary lobing 

 have been reported of many genera. The number of cotyledons 

 when fixed is fixed at two. Ceratozamia cannot be regarded as an 

 exception, for it is dicotyledonous in the proper sense of that term. 

 Among the Coniferales the tendency to reduce the cotyledons to the 

 fixed number two is even more striking, as indicated by series B of 

 fig. 462. Cupressus, Sequoia, and the Abietineae, which must be 

 regarded as the oldest members of the Pinaceae, are characteristically 

 polycotyledonous; while the more modern members of that family, 

 as well as all the Taxaceae investigated, are dicotyledonous. Ginkgo, 

 though older than the Cycadales and as old as the Abietineae, resem- 

 bles the former order in having fewer cotyledons; three is not an 

 uncommon number, but two is the usual one. In the modern order 

 Gnetales the fixed number is two. The inclination to revert to the 

 apparently primitive condition has not been lost by the angiosperms; 

 Anemone, Salicornia, and Oenothera are frequently found with three 

 cotyledons. 



"A second tendency that appears from comparative study is the 

 tendency to reduce the root poles to the fixed number two. In the 

 most primitive Abietineae and the more fernlike members of the 



