RELATION OF ALGAE TO DISSOLVED GASES. 197 
Fritsch (’09), in noting the seasonal changes of Clado- 
phora in Abbot’s Pool, near Bristol, England, describes the 
inflated type as characteristic of winter, and the much- 
branched type as characteristic of winter, late spring and 
summer; so it is a little difficult to interpret this or relate 
it to any reported conditions. 
A similar tendency was shown by one culture of Hydro- 
dictyon. In this the cells had all acquired a zigzag form, 
with inflated, club-shaped ends. They soon developed 
spores, or gametes, and disintegrated, with no further de- 
velopment. This was in an open jar of tap water which 
had evaporated to about one-eighth of its original volume. 
Freund (’08), in an extensive article on the influence of 
environment on vegetative reproduction, says: ‘More proba- 
ble, though less clear, is the influence of the oxygen content 
of water. The assertion that zoospore production can be in- 
duced merely by treatment with oxygen, as stated by Waltz, 
has been disproved by Klebs for Vaucheria repens and 
V. clavata. Simply by increasing the oxygen content in the 
surrounding medium, so far as our present knowledge goes, 
or may allow us to judge, no alga can be aroused to zoospore 
formation. On the other hand, has it not been accomplished 
by the removal of oxygen? Klebs made astudy of Vaucheria 
and Hydrodictyon, which indicates that many alge (Vau- 
cheria repens, V. clavata, Hydrodictyon, and Oedogonium 
diplandrum, Stigeoclonium tenue, Draparnaldia and Ulo- 
thrix zonata) can be induced to form zoospores if they be 
removed from flowing water to stagnant water, which in- 
dicates that reduction of oxygen in the medium is, in this 
case, the regulating responsible factor. The possibility of 
the influence of a reduction in oxygen is not excluded when 
alge like Botrydium and Vaucheria, growing in moist air, 
produce zoospores by moistening with water. Naturally, in 
this case, other influences come in, such as the absorption of 
water, etc., which were not previously distinguishable.” 
None of the cultures, so far as I could discover, showed any 
tendency to zoospore formation in response to the stimu- 
lus of oxygen or COz. The tendency toward periodic spore 
