1 2 Bower . — Studies in the Phytogeny of the Filicales. VI. 
to several of the same species. The absence of a double vascular system in 
them shows that there is nothing inherent in the Acrostichoid condition 
leading to that diplodesmic state ; and it throws into the greater relief 
what is seen in Leptochilus tricuspis , and accentuates its resemblance in this 
respect to Cheiropleuria and to Platy cerium. 
Passing to the sorus itself, sections show that it is uniformly spread over 
the whole lower surface, excepting the midrib and the extreme margins. 
Its constituents are sporangia and hairs : the latter are relatively incon- 
spicuous, and not nearly so numerous as those of Cheiropleuria. They are 
septate and branched (Text-fig. 5), but the branches are few and short, 
consisting usually of a single cell of somewhat glandular appearance. They 
iV 
Text-fig. 5. Hairs associated with the sporangia of Leptochilus tricuspis . x 125. 
Text-fig. 6. Part of transverse section of a fertile leaf of Leptochilus tricuspis, showing the 
diplodesmic structure and hairs associated with the sporangia, x 16. 
are barely one-third the height of the mature sporangium. The sporangia thus 
form the chief constituent of the sorus, and their closely serried heads are 
what are seen from without. They are found of various ages in juxtaposi- 
tion, and there is no grouping of the older sporangia which suggests any 
primitive soral relation (Text-fig. 6) : their orientation is usually so that 
the annulus lies in a plane transverse to the leaf. 
Comparing this with what is seen in Cheiropleuria , the hairs there are 
very numerous, 1 and are septate, but unbranched, and as long as the 
sporangia. Thus, as seen from without, the sporangial heads appear isolated, 
and packed in by the enlarged distal cells of the much more numerous 
hairs. Comparing, on the other hand, with Platycerium , the sori are there 
distinctly marked, as in P. Willinkii , or even isolated, as in some cases of 
1 Ann. ofBot., 1915, pp. 5*5 and 518, Figs. 15, 17. 
