46 SetchelL — An Examination of the Species 
which they inhabit. In more complex species they occur in 
groups or heaps somewhat contracted together. The step 
from such a condition to that shown in D. Niesslii , D. 
limosellae , or even in D. decipiens , is a gradual and easy one. 
The need for a covering of some kind for the sorus in the 
species with aquatic hosts is shown in D. limosellae , and to a 
much greater extent in D, decipiens , by the dense coat of 
browned and hardened hyphae. We find this covering sup- 
plied in D. hottoniae and species of true Doassansiae, by the 
transformation of the outermost spores to form the cells of 
the cortex. Otherwise the development of the sorus seems 
to be the same as in the preceding group. There are two 
sets of variations from the type of the group of the Eudoassan- 
siae ; in D. obscura , the central hyphae of the sorus remain 
undeveloped, while the cells of the outer hyphae are changed 
into the spores and the sterile cells of the cortex ; whereas in the 
species of the subgenus Doassansiopsis , the cells of the central 
hyphae have become swollen, but instead of developing into 
spores, have remained with their walls, have lost their solid 
contents, and so have become changed into a mass of paren- 
chymatous tissue. 
The genus Burrillia stands in about the same relation to 
the group of species represented by D. decipiens , that Doassan- 
siopsis does to Eudoassansia. Both groups lack the cortex ; 
and while the sorus of D. decipiens is readily separable into 
its component spores on crushing, the sorus of the genus 
Burrillia possesses a central mass of parenchymatous cells 
about which the spores are compacted so firmly as to be 
practically inseparable either from it or from each other. 
It is a difficult matter to determine the relation in which 
Cornuella lemnae stands to the other types. It may, perhaps, 
bear much the same relation to the D. decipiens group that 
Pseudodoassansia does to Eudoassansia . But the divergence 
between C. lemnae and D. decipiens certainly seems greater 
than, for instance, does that which exists between D. obscura 
and D. sagittariae. We may perhaps hope for some new 
form to throw more light upon the affinities in this case. 
