Morphology of Cycadean Sporangia. 425 
(Fig. 2). The part bearing the sori has increased in size, and 
its lateral lobes are more prominent Sori continue to arise 
toward the outer border of the lateral lobes, and also on the 
elevated median ridge. As the latter increase in number, 
they connect the two groups of sori which were at first 
separated by a considerable interval. Those last formed are 
the most regular in form ; they arise as circular elevations, 
the margins of which soon become distinct, and they are at 
first separated from one another by wider intervals than the 
earlier formed sori. The appearance presented by the latter 
(Fig. t) suggests an origin by unequal growth of a slightly 
elevated central region. 
The differentiation of the sorus into sporangia agrees 
closely with what takes place in Ceratozamia. On the same 
sporophyll all stages from the first indication of a sorus to 
sporangia of considerable size are present (Figs. 2, 3), while 
Warming’s figures suggest that the numerous sori on any 
sporophyll of Ceratozamia are at the same stage in their 
development 1 . 
One peculiar feature in the relation of the individual 
sporangia of a sorus to each other is best illustrated by 
a transverse 2 section (Fig. 4). In many cases the sporangia 
become equally distinct from one another at an early stage, 
but sori were frequently observed, in which some or all of the 
sporangia remained for a time united in pairs. In the sorus 
figured three such pairs are seen, the crosses indicating the 
position of the sporogenous groups of cells, which were similar 
to that shown in Fig. 8. 
The superficial cells of the region of the sporophyll, on 
which sori are about to arise, have larger nuclei and more 
abundant protoplasm than the underlying ones. The 
epidermis is a perfectly definite layer dividing only by 
1 Warming, Contrib. a l’histoire naturelle des Cycadees, Copenhagen, 1879, 
Tab. V, Figs. 2, 4, 8, 9, 10. 
2 By a transverse section of a sorus or sporangium is meant one parallel to the 
surface of the sporophyll. A surface perpendicular to the surface of the sporophyll 
will be spoken of as a vertical section and, when possible, will be distinguished as 
radial or tangential with reference to the sorus. 
