//. The Ovule of St anger ia paradoxa. 301 
Cycadean ovules and the microsporangia has been due to 
the ovules investigated having a marginal position on the 
sporophyll, while the microsporangia are usually borne on 
the under surface. In Stangeria (and the case is the same 
with some other genera) the ovule is clearly intramarginal, 
and careful comparison of the male and female sporophylls 
shows that as regards position the ovule clearly corresponds 
to a microsporangium or to a sorus of microsporangia. In 
seeking for evidence as to the homology of any structure, 
relative position, although important, must be confirmed by 
the study of the mode of development and by the structure 
of the organ when mature. With regard to the development 
considerable correspondence between the ovule and the sorus 
can be recognized in the early stages. The first stages of the 
ovules of Ceratozamia described by Treub, from which there 
is no reason to assume Stangeria to differ, show clearly that 
the sporogenous group of tissue has the same origin as in the 
microsporangium, though probably in the case of the ovule 
derived from more numerous hypodermal cells. Even in the 
ovule represented in Fig. 2 the continuity of the rows from 
the hypodermal layer to the base of the sporogenous group 
may be traced. The differences between the development 
of the sorus of microsporangia and the ovule only become 
pronounced when the arrest of growth in the region between 
the individual sporangia takes place, or (a mode of expressing 
the same fact which is probably more correct) when active 
growth becomes localized around each archesporial group. 
The comparison at later stages must be made between the 
individual sporangium and the ovule; in both a large oval 
mass of sporogenous tissue is developed, which is marked 
off more clearly by the flattening of the layers of cells 
immediately around, and readily separates at this region. 
Further, the comparison is perhaps justifiable between the 
persistent tapetal layer, derived from the outer layer of the 
sporogenous tissue in the microsporangium, and the layer 
which has the same place of origin in the ovule. The facts 
of development then would support the view that the ovule 
