1913] YAMANOUCHI—HYDRODICTYON AFRICANUM = 95 
turgidity, so that when the net is supported at one end, the entire 
plant is kept straight and can be held up in any position without 
bending or drooping. When the plants grow larger, the turgidity 
of the cells remains the same, but the connection between cells 
is by only a small portion of the surface and consequently it is 
impossible to move the plant without breaking the cells apart. 
As the plant grows, the connection becomes less and less secure, so 
vi 
Fic. 1.—H ydrodictyon africanum, showing successive stages of development: a, 
May 2, 1912; b, May 12; ¢, more 20; d, June 12; e, June 20; f, October 12.—Sketches 
_ from living material, natural size 
that the cells fall apart at the slightest touch or even by a move- 
ment of water caused by small crustaceans, until finally the nets 
are broken apart into solitary cells, or coenobia. During this 
_ development, the coenobium has reached an enormous size, the 
_ diameter often being more than 1.5 cm. Sketches from living 
material in successive stages from late April to the middle of June 
_ are shown in fig. 1. 
