148 



THE AMEKICAIS MONTHLY 



[August, 



the fresh-water algge the error com- 

 mitted by the author was unavoidable, 

 but such errors are now less excus- 

 able, since we have learned more of 

 the life-history of these plants, of the 

 singular transformations they undergo 

 in a kind of intermediate existence, or 

 arrested development, a condition 

 between the embryonic microspores 

 and the perfected plants — a condi- 

 tion which often continues for 

 months, during which time they as- 

 sume various forms, most commonly 

 unicellular forms — which have given 

 rise to numerous false genera. 



Our lamented friend the late Dr. 

 Rabenhorst, of Prussia, published a 

 most valuable summary of the fresh- 

 water algse, which included the names 

 and descriptions of all forms known 

 up to the date of his publication. He 

 performed a noble work, but more 

 exact information acquired in later 

 years reveals that hundreds of his 

 described forms are mere intermediate 

 or temporary life-conditions. They 

 are often found in large numbers — 

 we may say, in myriads. They fre- 

 quently hold very tenaciously to their 

 intermediate forms, passing through 

 a cycle or through cycles of existence 

 ere they round out into the true, per- 

 fected plants. 



With these facts, certainly known 

 to our author, it seems hardly credi- 

 ble he should have wasted so much 

 learning to uphold a chimera. 



To us his efforts, in a previous num- 

 ber of the same journal, to uphold 

 the unicellular algae as stable forms, 

 appear equally unreasonable; they are 

 constant for a season, yet is their 

 chief characteristic that of great 

 changeability. 



Dr. Cooke, of London, has com- 

 menced the publication of the 

 " Fresh-water AlgcE of Great Britain." 

 The work appears in numbers. The 

 plates are prepared with an eye to 

 beauty, and the letter-press is made 

 attractive ; but it is to be regretted 

 he does not give sufficient promin- 

 ence to the instability and doubtful 

 character of many of the forms al- 



ready presented. Earlier authors 

 have put forth much more advanced 

 views. 



One of the most masterly studies 

 was made by the late Dr. H. Itzig- 

 sohn, of Russia. His essay on Hapa- 

 losip/wn Braunii reveals a profundity 

 of research into the life-history of a 

 single plant, and displays the many 

 forms which occur in its develop- 

 ment. There is a similar history, 

 perhaps, in many cases unwritten, be- 

 longing to many other forms. 



Why should these be ignored, and 

 the primitive notions be upheld with 

 such tenacity ? F. Wolle. 



Aquaria for Microscopists. 



In the management of small aquaria 

 a very little experience is of great 

 value. The first attempts are usually 

 not successful, but after a while it 

 will be found that the aquaria run 

 along without much trouble. The 

 secret of this is in the experience, 

 which seems to have come very natur- 

 ally, that indicates to us just about 

 how much plant-life should be in a 

 given quantity of water, and where 

 the aquarium should be placed to 

 ensure the most satisfactory growth. 



It need not be said that the con- 

 ditions of prolific growth in an aquar- 

 ium are the same as are found in 

 open ponds, but to imitate those con- 

 ditions indoors requires some judg- 

 ment. The collector will observe 

 that the water in ponds, although 

 freely exposed to the glare of the sun, 

 never becomes greatly heated, because 

 of the rapid evaporation from the 

 surface. But if an ordinary aquar- 

 ium be thus exposed to the sun, the 

 small body of water would soon be- 

 come so warm that many organisms 

 would die in it. Therefore, the 

 aquarium should not be placed in 

 sunlight. By far the best place is near 

 a window where it can receive good 

 light from the sky all day long, but 

 no direct sunlight. The first, and 

 most important rule is, keep the water 

 cool. 



