245 
$ 13. Dioon edule Lindl. 
Literature: Chamberlain (46). 
Figure: 46 p. 356. 
The female strobilus of Dioon is formed by an axis 
bearing sporophylls, placed in spiral order. These are 
composed of a stalk with a peltate lamina at its top, 
which bears two ovules at its under surface. The lower 
sporophylls of a strobilus do not bear ovules or at least 
slightly-developed ones. In ripe condition the ovules have 
an orange colour. 
The sarcotesta is not sharply marked off from the 
stony-layer, and it is not possible to separate them. As 
in Cycas the epidermis has thickwalled cells, whilst in the 
underlying tissue many tannine-cells and large mucilage- 
canals are present. 
In the sclerotesta four layers are to be destinguished 
according to Chamberlain, principally characterized by 
an other orientation and form of the cells. 
The endotesta is well differentiated from the stony 
layer, and in a young condition it reaches a considerable 
thickness, but in a ripe seed the inner flesh is reduced to 
a thin dry membrane which peels off easily. 
The nucellus is for a small portion only free from the 
endotesta and protrudes into the micropyle with a rather 
sharp beak, in which lays the pollenchamber. ,, The beak 
closes and hardens immediately after pollination” (p. 335). 
Two vascular bundles enter the base of the seed each 
of which divides into a branch running in the sarcotesta 
and one in the endotesta. Those in the outer fleshy layer 
often divide into the lower part, but then continue their 
way in a straight direction to the micropyle. Their total 
number is about fourteen. The bundles of the innermost 
system divide at a greater height, and on a transverse 
