LABORATORY AQUARIUM. 213 
What are the conditions of the best collecting grounds in the 
field? I have often observed the tendency of collectors of 
rivers and lakes, and pna and have very often seen them 
enemies. Moreover, the period of rest pee the dry ferreus 
seems necessary to preserve the vitality of some algae. It is 
a matter of mast ris that few microscopic plants grow in 
large bodies of water, except Cladophora Hydrodictyon, Drap- 
arnaldia, Chaeto phora, Chara. To prove how fish relish spi- 
rogyra, a small amount may be put in a globe with goldfish 
and it will rapidly be eaten 
Many collectors attempting laboratory cultures in aquaria 
have somehow got passessed of the idea that the water must 
be changed to prevent decay. Ihave thoroughly vain this, 
ut too much emphasis can not be laid on the m 
doxical as it seems, few plants can ee such tr MUCH AE and 
most will either die or be much retarded i Fortes ent. A 
moment's reflection will tell us the reaso I have said that 
microscopic plants find great difficulty in fe is deme er 
to surroundings, because being so small, they are benefitted 
or injured by insignificantly small factors, and it is just be- 
cause they dice great difficulty in accommodating ión 
to new environment that we must refrain from putting them 
in a new condition by daily changes of water. In the second 
place, when plants are present in healthy condition, the very 
oxygen they give off is a check on bacteria, and whe heal 
they can keep the water purer in this way than we can by 
enga it. Water is not impure because green plants grow 
it. Moreover, green plants are put in fish aquaria in order 
to keep the water oxygenated. 
en it is necessary to bring fully developed plants into 
the laboratory aquarium from the field, they should be allowed 
to remain in the water taken from their habitat, unless there 
is a chance of a new generation developing. Some algae may 
stand the changes of water once, many promptly rebel and die. 
We may then take the chances ‘of getting a new culture from 
the spores produced as the plants disappear. In any case, by 
keeping all cultures several months before throwing out a jar 
