330 BOTANICAL GAZETTE [NOVEMBER 
other cycads reach their full size without the stimulus of pollination. 
‘However, the only greenhouse cone of Dioon which has come to 
my notice had only abortive ovules, and in the field the ovulate cones 
at any considerable distance from staminate plants are likely to 
contain only abortive ovules. Such ovules have not been pollinated. 
In cones bearing ripe seeds the abortive ovules have usually been 
pollinated, but have failed to develop from lack of room or of 
nutrition. It is easy to determine whether pollination has taken 
place, since the course of the pollen tubes is marked by conspicuous 
brown lines upon the nucellus. ; 
The youngest ovules secured in 1904 were sent from the field 
November 1. These were 1°™ in length and showed the archegonium 
initials. Only one small cone had ovules as young as this, the ovules 
in other cones of this date measuring 1.5°™ in length and showing 
the central cell of the archegonium. November 14, six weeks after 
pollination, the average length of the ovules is about 2.3°"; in the 
following spring (April 3), when the ovules had reached their full 
size, the largest ones measured 4°™ in length and 2.2°™ in diameter. 
The average length is about 3°", and the diameter 2°™. Many 
ovules are nearly spherical, measuring about 3°™ in length and 2.8°™ 
in diameter. The ovules are perfectly smooth, and until nearly ripe 
are white, but become cream-colored or yellowish when exposed to 
the air; at maturity they have an orange color which contrasts 
sharply with the pale yellow of the naked portion of the sporophyll. 
They are sessile, but many of them appear to be stalked because 
strains due to the growth of the sporophylls and ovules draw out 
the base of the sporophyll into a stalk-like structure (jig. 5)- 
The ovule of Dioon reaches its full size before the stony layer 
becomes hard enough to occasion any serious difficulty in sectioning. 
Median longitudinal sections 3 or 4™™ in thickness, well dehydrated 
and cleared, but not stained, are best for a study of the general topog- 
raphy (fig. 10); while fresh ovules whose bundles have taken up 
eosin are most convenient for tracing the vascular system (jigs: 7; 9 9)- 
The epidermis is smooth, strongly cutinized, and contains no stomata. 
At the base of the ovule the abscission layer is marked by a distinct 
constriction (fig. 10, @). The opening of the micropyle is amber Or 
brownish in color from the drying of the pollination drop which, 
