98 BOTANICAL GAZETTE [ FEBRUARY 
subject to so much movement that it might be called running 
water. This then is the probable reason for the arrangement of 
the plants. The preference of Chetophora for quiet, pure water 
is known, while Lyngbya and Dichothrix flourish in waters either 
with or without a current. 
The Chztophora thalli are strongly impregnated with lime 
and are hard, making decalcification necessary before exami- 
nation under the microscope. The nature of the calcium 
carbonate in these thalli differs from that in the substratum. 
Here it appears in the form of crystal plates which, under the 
high power of the microscope, have a striated appearance. This 
results from the fact that they have running through them per- 
forations or tubes corresponding in size and form to the Cheto- 
phora filaments. Branches of the Chetophora may be observed 
indeed entering these tubes and emerging at the opposite side 
‘of the crystal plate (p/. LX, fig. 6). If a longitudinal section 
be cut from a thallus and placed under the lens, the crystal 
plates being left intact, it will be seen that these pipes or tubes 
radiate from the center, following exactly the trend of the 
branches and for the most part containing the branches, though 
it is somewhat difficult to focus closely enough to observe the 
latter point with the thick crystals under the coverglass (pl. IX, 
hg. 7)- : | 
he Chetophora, as well as a thin growth of the blue-green 
plants, occurs on dead limbs which have fallen into the water 
from the trees on the banks. A few of the twigs taken out of 
the tank late in the autumn displayed after drying a violet tint 
on their under surface. This was caused by the presence of a 
small Chantransia, which, like the other alge, was incrusted 
with lime. Its color when growing was probably green, since 
otherwise it would have been noticed before it was dry. It was 
accompanied by both the Lyngbyas, similar in all respects to 
those found in the stratum on the sides of the tank, with the 
exception that their cell contents had now assumed a bright 
violet color. In rare cases filaments were still found with the 
_ former zruginous tint, and some belonging to the larger species 
