338 BOTANICAL GAZETTE [NOVEMBER 
extensive sporogenous tissue in the ovule, and believes that the outer 
portion of it gives rise to the tapetum, while all the tissue within 
except the functional megaspore disappears. Unfortunately, no such 
early stages were secured in Dioon, but since the jacket surrounding 
the microspores may originate from either sporogenous or sterile 
cells, there seems to be no objection to regarding the jacket sur- 
rounding the megaspore as equivalent to that surrounding the micro- 
spores, especially since homosporous forms, to which all heterosporous 
forms must ultimately trace their origin, have well-developed jackets. 
Base oj the ovule——The lower limit of the ovule is marked super- 
ficially by a slight constriction as soon as the abscission region begins 
to develop (fig. 10, a). This region does not extend straight across, 
but is depressed in the center, with the depression away from the body 
of the ovule. When the ovule breaks off, the slight protuberance at 
the base is due to the shape of the abscission zone. This zone, about 
twelve cells in thickness, consists of nearly isodiametric cells, and 
thus contrasts rather sharply with the elongated cells above and below 
(fig. 14). Almost as soon as the zone can be distinguished, inter- 
cellular spaces appear, which increase in size until they sometimes 
become as large as the cells themselves, making them appear some- 
what like the stellate cells of Typha, Scirpus, and similar forms. 
These cells are rich in starch. Above the abscission region the axis 
of the ovule extends upward and terminates in a conspicuous pro- 
jection which occupies a deep pit in the stony layer. This projection, 
which was described as the Einstiilpung by Miss Stopes (15), may be 
called the basal papilla (fig. ro, p). In the unripe seed the tissue of 
the basal papilla is noticeably tougher than that of other portions of the 
outer fleshy covering. In the ripe dry seed it looks for a time like a 
toothpick broken off in the stony layer, but it soon decays like the 
rest of the fleshy layer and its place is marked by a conspicuous pit 
about 2™™ in diameter and extending almost through the stone. 
Large elongated cells containing tannin are abundant on both sides 
of the abscission zone, but they do not extend into it. Several large 
mucilage ducts, which lie within the region occupied by the vascular 
bundles, reach almost to the top of the basal papilla. In the position 
and shape of the abscission layer and also in the appearance of the 
basal papilla, Dioon resembles Lagenostoma as described by OLIVER 
