84 BOTANICAL GAZETTE [AUGUST i 
than the Bennettitales, and were much more scantily represented dur- — 
ing the Mesozoic; and therefore the latter alternative seems to be the — 
more reasonable. In any event, the only question at issue is whether — 
the gymnosperm stock which came from the Cycadofilicales into the 
Mesozoic is to be called Bennettitales or a Bennettitales-Cycadales — 
plexus (a “common stock”); and it is altogether probable that this : 
stock has already been assigned to the Bennettitales in the description | 
of cycadophyte forms from the Triassic and Jurassic. In the 
gymnosperm flora of today, therefore, the Cycadales, although — 
relatively a modern group, are the nearest representatives of the : 
Paleozoic Cycadofilicales. E 
The Ginkgoales and Coniferales have both been traced into late 
and independent Paleozoic connection with the Cordaitales, and were — 
well displayed during the Mesozoic. The Ginkgoales, while widely 
distributed during the Mesozoic, apparently were never a large — 
group; and this group has continued as a single line into the present — 
flora, and has retained certain features of the Cordaitales which the : 
Coniferales have lost. The Coniferales, on the other hand, began — 
that extensive differentiation during the Mesozoic which has resulted 
in six recognized tribes in our present flora. Among these tribes the — 
earliest to be recognized are the Abietineae and the Araucarineaés 
and their very early separation is so evident as to raise the question — 
whether they may not be independent in origin. In any event, the : 
other tribes recognized in our present flora were of later origin; the : 
Taxodineae and the Cupressineae, and possibly the Taxineae, arising — 
from the Mesozoic Abietineae; and the Podocarpineae possibly 
arising from the Mesozoic Araucarineae. : 
The connections of the Gnetales are altogether obscure, and : 
every opinion as to their origin must be regarded as very tentative. : 
Although they have not been discovered as fossils, the great amount — 
of differentiation they show and their widely scattered geographical : 
distribution indicate a considerable history. Evidence seems to © 
accumulating that they may have been derived from the Cupressinea® — 
or at least that they are closely related to that tribe in origin. - 
VASCULAR ANATOMY S 
ve 
The central cylinder of the Cycadofilicales, like that of ferns, 
was protostelic, siphonostelic, or polystelic. Whatever may be “ 
RE 
