MIDLAND NATURALIST. 95 
added from time to time to supply what has evaporated but the 
amount added at any one time should never exceed one fifth of the 
total contents of the jar, or the plants may be either killed or seri- 
ously retarded in their growth. The water added contains enough 
salts in solution to last the growing plants for some time. Another 
method of replacing food removed from the jars in the process of 
growth is to add the salts directly in the proper proportions as 
shown by Sachs. Such plant food can be obtained in the form of 
tablets* and one can be added to a jar every few months. For 
algae one tablet to every quart of water contents of jar added oc- 
casionally gives good results, and is a safer method than adding 
fresh water, the shock of which often proves fatal. In supplying 
water removed by evaporation, care must be taken that the water 
when taken from taps be free from rust, and that accordingly the 
the water be only taken afterit has run for some time. Iron is 
fatal to Conjugatae. It has been found that it is dangerous or de- 
structive to such a hardy plant as Marsilia vestita, one of the 
Pteridophyta. 
method of obtaining or rather preserving algae alive depends 
on a principle just opposite to that of ''forcing." A considerable 
number of typical algal forms appear in summer or autumn when 
they cannot be used for demonstration. Among these are /7yd»o- 
dictyon and Spirogyra nitida. By putting these late fruiting 
plants in a jar in a normal diffusive light in a cool place they will 
last for months with little change. Spirogyra nitida I have thus 
kept in fruiting condition till spring, and this plant usually starts 
zygospore formation at the end of September. Hydrodictyon plants 
have also been kept in a cool well lighted place without decay until 
Spring. The reproductive stages at maturity remain a long time 
unchanged, and are not so subject to decay as vegetative stages. 
It might not be an entirely unprovitable procedure to attempt the 
arrest of the growth of plants in desirable stages until needed for 
demonstration. It might be of interest to find to what extent 
living plants will submit to preservation in mild state of cold stor- 
age until needed for class work 
In regard to collecting algae from the field for class use best 
results are usually obtained in Spring. Most of the useful plants 
for class study appear then in our latitude but many remain or re- 
AAA tablets can be obtained at very reasonable terms from Mr. E. F. 
Bigelow, Arcadia, Sound Beach, Ct. 
