186 MISSOURI BOTANICAL GARDEN. 
water. From these experiments he concluded that Celas- 
trum in well aérated water will form free. cells, but in 
stagnant water will form cenobia. He had gotten similar 
results from hanging drops of cane-sugar solution. Those 
which he stirred vigorously and mixed with air produced free 
cells only, while the unstirred solution formed ccenobia. 
The stirring had mixed in a considerable amount of air which 
had remained. 
In order to test this further he arranged cultures in Erlen- 
meyer flasks (0.2% Knop’s solution), likewise in open 
dishes. He boiled them to drive out all the air. After 
cooling, the flasks were closed and either oxygen or carbon- 
dioxide let in (manner not stated) to about half (14) pres- 
sure, kept air-tight under water, and shaken so as to mix as 
much as possible and saturate one solution with one respective 
gas (Oz or COz). A little of the alga in four-celled colonies 
from pure cultures was then introduced by means of a curved 
pipette, and the flasks then closed air-tight with paraffine. 
There were eight flasks in all; four with oxygen and four 
with carbon-dioxide. Two each were placed in the light and 
two each in the dark. After six days those with oxygen 
showed many free cells but no ceenobia. In the flasks with 
carbon-dioxide only a few of the 4-celled conobia had 
changed; but in two weeks many 8-celled ccenobia appeared. 
Those with Os, left in the dark eight days, showed no change. 
Those with COs, left in the dark eight days, were developing 
daughter cells the same as those left in the light. Similar 
results were obtained with certain species of Scenedesmus; 
oxygen cultures yielded only single free cells, while cultures 
with COz produced four-celled ceenobia when grown in tall 
13 em. cylinders. Likewise with Dictyospherium; if the 
culture solution after sterilization was not shaken or aérated, 
many-celled coenobia resulted—some even as high as 100- 
celled; while similar cultures at the same time, but shaken 
after sterilization, to secure aération, yielded only single-celled 
colonies, or a few 4-celled to 16-celled ones. In the latter the 
cells stood farther apart, while in the former they grew more 
closely together. 
