Bower.—Studies in the Phytogeny of the Filicales . 
519 
Moreover, it is not always equally clear that the annulus is continuous 
past the stalk. Such differences are natural, and are even to be anticipated 
in cases like the present, where, ex hypothesis the sporangium has undergone 
modification from a more primitive type. 
For comparison with the above, the sporangia of Platycerium have 
been examined, and a typical example is shown in 
Text-fig. 18, a , for P. aethiopicum. One point of 
difference is in the stalk, which here consists of only 
three rows of cells, as is clearly indicated by trans¬ 
verse sections (Text-fig. 18, b). The form of the 
sporangial head is more pear-shaped, and the annulus 
less clearly oblique, while it retains the lateral 
position of the stomium distinctly below the equa¬ 
torial line. Opposite the insertion of the stalk the 
annulus is drawn down into an acute angle, in ac¬ 
cordance with the pear-like form of the sporangium, 
and it is almost interrupted, but not actually so ; for 
the rather elongated cells on either side do, as a 
matter of fact, retain contact, as is shown by the 
dotted lines in Text-fig. 18, a. Comparing this 
sporangium with that of Dipteris or Cheiropleuricts 
it is seen to be of a more advanced type, as shown 
by the thinner stalk, the more vertical annulus, 
and the almost completed interruption of it at the 
insertion of the stalk. 
C8 
b. 
Text-fig. 18. a, spo¬ 
rangium of Platycerium 
aethiopicum as seen from 
the side. b, transverse 
sections of its stalk, x 80. 
Development of the Sporangium. 
Unfortunately the material of Cheiropleuria did not, in age or in 
preservation, suffice for tracing the development of the sporangium fully. 
But the essential features have been observed, and a comparison may be 
drawn with the very similar development in Dipteris conjugata. The 
general features of the fertile leaf have been described above. If sections 
of the fertile region be examined, the flattened expansion is found to be 
relatively thick, and it has a spongy texture of the mesophyll towards the 
upper surface. The mesophyll is traversed by two distinct types of vascu¬ 
lar tissue; first, the normal venation, lying in a median plane, and with the 
small and ' compact strands clearly circumscribed by parenchymatous 
sheaths. Two of these strands are shown, right and left, in Text-fig. 15. 
Secondly, there are found lying between these, and closer to the lower 
surface, more lax strands composed of larger tracheides of the storage type, 
and without parenchymatous sheaths. These are the receptacular endings 
of veins, which, as seen in surface view, are liable to be greatly enlarged 
and elongated (Text-fig. 12). 
M m 
