254 Bower. — Imperfect Sporangia in certain 
In the embryo the first traces of a sporangium may appear. 
They are certainly absent from the first-formed leaves of the 
young plant 1 . 
PSILOTACEAE. 
In Tmesipteris there is commonly a sterile region of some 
length at the base of the aerial shoot ; in its upper part, 
fertile and sterile zones may alternate without any definite 
regularity. The zones are, however, excessively irregular in 
Tmesipteris ; thus an odd synangium, or two' or three, may 
be interpolated in a sterile region, or odd sterile leaves 
may occur in a region that is mostly fertile, a condition which 
has been found in some species of Lycopodium. 
The length of the leaf does not depend upon the presence 
or absence of a synangium ; fertile leaves often equal in length 
the sterile ones. But there is usually a general diminution 
of the size of the appendicular organs at the upper limit of 
the fertile region (especially where that region is long) which 
affects both organs alike. This condition resembles that of 
the less differentiated species of Lycopodium, of the Selago , 
and sub- Selago groups. 
Arrested or imperfectly developed synangia are not un- 
common, especially at the limits of the fertile zones 2 . They 
appear as small growths in the normal position on otherwise 
fully developed parts. They are susceptible of the same 
interpretation as the imperfect sporangia of Lycopodium. 
In P silo turn the distribution of sterile and fertile regions 
resembles that in Tmesipteris , successive zones being found 
on the same branch, while the various branches of one shoot 
show a synchronism, in the limits being at the same levels 
in each ; as is the case also in some of the Selago group of 
Lycopodium. Partially or completely abortive synangia are 
found especially about the limits of the fertile zones ; and 
Solms-Laubach 3 notes the intermediate types of leaf between 
1 Campbell, Mosses and Ferns, Figs. 149-153. 
2 Bertrand, Arch. Bot. d. Nord, vol. i, p. 475 ; Bower, Phil. Trans., 1894, B., 
p. 544, and PL LII, Figs. 149-153. 
3 Solms-Laubach, Buit. Ann., vol. iv, p. 174. 
