82 
oo _ by the bacteria and other micro-organisms, 
s, t 
in detail, while the shelves of the case are occupied by the actual 
specimens still attached to the substances on which they grew. 
Most of the specimens are small and very delicate, in fact some 
are so fragile that a mere breath of air will ruin them, but a few 
are quite coarse. We now have an excellent example of one of 
the large forms, obtained from a great mass which several years 
I E g 
at the back of the cases, and additional specimens preserved in jars 
on the shelves. The plants of this series are much more variable 
in form than those of the preceding series and are also much more 
numerous. Some forms are unicellular and microscopic, others 
ful that their remains now form almost inexhaustible deposits of 
diatomaceous Our exhibition photographs came from 
United States War Department, whil r specimens came fi 
the various deposits in Nort merica, Near is Sphaerella 
and its relatives, minute plants growing on the bark of trees or 
