214 AMERICAN MIDLAND NATURALIST. 
which seems to be unproductive for a time, we often find some 
remarkable growths later. Absolute decay by bacteria indi- 
cated by changes of color and offensive odors as also complete 
choking up of the contents by oscillatoria are the signs that 
the contents of a jar are beyond the stage of future usefulness. 
The reason why the "forcing" method is the best is the fol- 
lowing. Mud collected in the field in dry or adverse condi- 
tions, even in winter, contains spores which seem in the rest- 
ing stage eagerly awaiting a chance to develop. "They will 
come out even under comparatively unfavorable conditions or 
will then make a special effort, to accommodate themselves to 
even a possible existence. They will even develop in the lab- 
oratory in winter, because the change from the field to warm 
room is not unlike the advent of spring to them, especially if 
the light is strong. Resting stages contained in the mud can 
more easily resist adverse conditions. Plants and animals go 
into the resting stage or form ee for this very rea- 
son of ee adverse conditio 
Plant aquaria should be aed with a plate glass, both 
. to Fo out dust and also to prevent rapid evaporation. Water 
will evaporate slowly despite all effo rts. This must be re- 
placed little by little. Adding too large an amount at one time 
may prove fatal. The addition is also necessary to keep up 
the avala food salt of the plants. Addition of water must 
never exceed one-fifth of the contents of the aquarium. The 
salts used by plants and present in all natural water may be 
also replaced by-adding Sach’s tablets, as these contain the 
p proportion of mineral salts necessary to their develop- 
T Good light, in fact very strong, and direct sunlight is ne- 
essary to many algae. The average material develops well, 
however in diffuse sunlight. I have tried for some years to 
p cultures of Euglena, Pandorina Haematococcus or 
Spier te in the laboratory but without success, and have 
finally found that my failures were due to want of sunlight. 
These plants, I have already shown, grow best in midsummer 
aces where organic matter is decomposing in direct blist- 
ering sunlight, e. g. the wallows of pigs, pools around water- 
ing places, and near barns. I have once seen a basin of water 
containing manure at the bottom and covered one-half an inch 
deep with the Englena. This pool about 30x60 feet square 
was covered by a layer of the purest culture of Euglena. I 
have even found in the motile stage. It would be a pretty 
problem of mathematics to attempt to calculate the number 
of organisms present when we reflect that the animal, as you 
