THE PAST HISTORY OF MONOCOTYLEDONS 1 79 



of fossil plants, including not only ferns, cycads, conifers, Ginkgo, 

 etc., but such monocotyledons as Arundo, Potamogeton, etc., and 

 dicotyledons, e.g. poplar, myrica, oak, fig, walnut, plane, dogwood, 

 magnolia, eucalyptus, ilex, buckthorn, cassia, etc. 



In the Potomac formation of North America, again, and the 

 Laramie group an extensive flora occurs. Fifty per cent, of the 

 Angiosperms discovered are referred to existing genera or species, 

 e.g. oak, willow, birch, plane, poplar, maple hickory, fig, tulip-tree, 

 sassafras, laurel, cinnamon, buckthorn, and palms, e.g. Sabai, Fla- 

 bellaria, as well as other nionocotylede^ns and cycads, conifers, etc. 



In the Potomac formation 198 genera and 737 species of plants 

 were found, and of these 8 are monocotyledons. There are, moreover, 

 92 genera and 320 species of dicotyledons. Of these Geikie remarks : 

 "Of these higher forms of vegetation the more peculiar seem to be 

 what are known as ' generalised types,' indicating the great antiquity 

 of the flora." Amongst the dicotyledonous genera are Aralia, 

 Ciiuiainomum, Ficus, Hedera, I/ex, Juglans, Lai/rus, Magnolia, 

 Myrica, Platanus, Quercus, Rhatnnus, Salix, Sassafras, Vibirnum. 

 Thus both monocotyledons and dicotyledons appear upon the same 

 horizon. Are the former an offshoot of the latter, which are so far 

 as we know most predominant, or are the latter an offshoot of the 

 former? Are the monocotyledons monophyletic, and derived from 

 dicotyledons, and are these in turn descended from a primitive pro- 

 Angiosperm ? This question may be best discussed at this stage by 

 reviewing the different theories as to their origin. 



In an article upon the " Phylogeny and Taxonomy of the Angio- 

 sperms," ^ Mr C. E. Bessey approaches the subject from three points 

 of view: (i) historical, (2) ontogenetic, (3) morphological. In regard 

 to (i) statistics are given as to the percentages of monocotyledons 

 recorded by Schimper, Lesquereux, and Durand, from the Triassic 

 to present times. We reproduce only those referring to Cretaceous 

 and later epochs, since earlier forms are doubtful or erroneously 

 regarded as monocotyledons. 



In regard to these, Bessey remarks, " making due allowance for 

 possible errors of determination, we find that by the end of the 

 Jurassic period the monocotyledons were probably represented by 

 members of the groups (orders) Apocarpse, Coronariese, Calycinse, 

 and Glumace^. 



" To these we may add, in the Cretaceous,- a few representatives of 

 theEpigynae. It is interesting to note that the monocotyledonous plants 

 of the Tertiary have been referred mainly to the hypogynous orders, 

 and that none have been identified as representing the Microspermae. 

 .Apparently the evolution of the monocotyledons began with hypo- 

 gynous species and proceeded toward those in which epigyny is 

 most marked. Orchids are doubtless of very late evolution, so late 

 in fact that none have been preserved as fossils." ^ 



^ " Botanical Gazette," 1S97, pp. 145-178. 



2 We exclude pre-Cretaceous plants. 



•' ]'ide, however, notes under this heading, ante. 



