412 BOTANICAL GAZETTE [DECEMBER 
While it is hardly safe to arrange the three species in an evolu- 
tionary sequence before the life histories have been studied, it seems 
to me that D. spinulosum is the oldest and D. edule the most recent, 
so that the series should be D. spinulosum, D. Purpusiui, and D. edule. 
In favor of this sequence it may be said that D. spinulosum has a 
spinulose leaf throughout its life history, while D. edule shows the 
spinulose character only in the seedling, the later leaves gradually 
becoming entire. D. Purpusii has a leaf which is slightly but con- 
stantly spinulose in the adult plant. Its seedling is not known. 
Regarding the spinulose character of the seedling leaf of D. edule 
as due to recapitulation, D. edule is a later development than D. 
spinulosum and has come either from D. spinuloswm or from some 
unknown form with spinulose leaves. The leaves of D. edule and 
D. Purpusii present about such characters as we should expect in 
D. spinulosum, if this species should be brought from its well 
shaded habitat into the dry hot places where the other two species 
are found. 
I believe that throughout the Cycadales there has been a gradual 
reduction in the number of sporangia on a sporophyll. On this basis 
the sequence would be as I have given it. 
On the other hand, it must be admitted that in D. edule the ovulate 
cone is not so compact and the megasporophylls have not lost so 
completely the character of the vegetative leaf, which must be assumed 
as the ancestral form of both kinds of sporophylls. 
Since the original description of D. spinulosum was necessarily 
inadequate and incomplete, it seems worth while to describe the species 
from the more abundant material now available. 
DI0oN sPINULOsUM Dyer.—Adult plants 2-16™ in height; stem slender, with 
conspicuous transverse ribs, and a single zone of wood; leaves 1.5-2™ long, 
curved, with 80-117 leaflets on each side; leaflets 15-20°™ long, ro-15™™ wide, 
with 5~8 spines on each margin, the lower ones gradually reduced to mere spines; 
first leaf of seedling with as few as a dozen leaflets on each side, the leaflets with 
only 2-6 spines on each margin, lower leaflets not at all reduced; ovulate 
strobilus cylindrical ovoid, 35-50°™ in length, 20-27°™ in diameter; sporophylls 
densely hairy, closely imbricate, the exposed portion rounded or obtuse at apex; — 
seeds smooth, white, 4-5.5°™ in length, 2.5-3.5°™ in diameter; staminate 
strobilus elongated ovoid, 21°™ in length, ro°™ in diameter; exposed portion of 
sporophyll hairy, obtuse; microsporangia about 750 on a sporophyll. 
