418 BOTANICAL GAZETTE [MAY 
cycad characters. He notes the multiple leaf traces of the Medullosae, the 
concentric bundles in the rachis of Lyginodendron and Heterangium, and in 
the leaf of Sutcliffia; and among the cycad characters, the double leaf trace 
of Lyginodendron, and the secretory canal system. The leaves belong to the 
leathery type of recent ferns. The thickness and inrolled margins are xero- 
nie 0 characters, and the prevalent hypodermal sclerenchyma is xerophytic. 
CADALES.—The review of the literature of the cycad leaf is particularly 
thor probably because there have been two rather extensive investiga- 
tions. In the various genera and species, the shapes of cells of the epidermis, 
the sinus the parenchyma, the thick-walled cells, and the vascular system 
are treated under separate headings. The xerophytic features are emphasized. 
The leaf structure is so characteristic in the different genera that a taxonomic 
key, based upon leaves, is presented. Since no study has been made of the 
leaves of Microcycas, this genus is not mentioned. Doubtless most of the 
investigations have been made upon leaves taken from greenhouse specimens. 
ile the general structure is probably about the same as in plants in their 
native habitats, we should expect to find the xerophytic characters more 
pronounced in plants exposed to the extreme xerophytic conditions than in 
greenhouse plants, which are more or less shaded and are frequently watered. 
BENNETTITALES.—So little is known of the internal structure of the mature 
leaf that this section is very brief, but there is a mixture of fern and cycad 
characters, and, according to FEUSTEL, some angiosperm characters. 
ORDAITALES.—This order is treated under the separate headings Por- 
oxyleaé, Pityeae, and Cordaiteae; but since no leaves are known in the Pityeae, 
the study deals only with the other two groups. Resemblances to some of 
the Cycadofilicales and to some of the recent cycads are pointed out, but it is 
very questionable whether the similarities are due to relationship. Resem- 
blances between the leaves of Cordaites and some of the Coniferales, especially 
Agathis, seem more striking 
GINKGOALES.—The betes leaves of Ginkgo are significant, the 
lobed and divided character being retained from the ancient forms. The 
structure of the leaf, with its long petiole, broad blade, and soft consistency, 
is not very xerophytic, but indicates that Ginkgo in its phylogeny has come 
from a climate with long wet periods. 
CONIFERALES.—The structure and biology of the leaf of Pinus are treated 
in great detail as a type of the order, and the other genera are considered from 
the standpoint of comparative morphology and biology. The leaves of all the 
conifers, by their form, structure, and consistency, are protected against wind 
and rain. They are both xeromorphic and xerophytic. Several ecological 
hypotheses are advanced to account for the geographical distribution of the 
group. 
GneTALEs.—Naturally, the genera of this group are treated separately; 
but, in spite of the striking differences, the three genera show more resem- 
blances to each other than to the rest of the gymnosperms. The leaves of 
