ON FRESH WATER ALG.E. 93 



scum to be seen floating on ditches. Portions of this should be 

 preserved, as it frequently contains interesting Nostocs and other 

 plants. 



In regard to large rivers, the time of year in which I have been 

 most successful in such localities is the latter summer months. 

 Springs and small bodies of clear water may be searched with a 

 hope of reward at any time of the year when they are not actually 

 frozen up. I have found some exceedingly beautiful and rare 

 Alga3 in such places as early as March, and in open seasons they 

 may be collected even earlier than this. The Desmids are most 

 abundant in the spring, and possibly most beautiful then. Tiny, 

 however, rarely conjugate at that time, and the most valuable 

 specimens are therefore to be obtained later — during the summer 

 and autumn months, at least, so it is said ; and the experience I 

 have had with this family seems to confirm it. Rivulets should be 

 watched especially in early spring, and during the summer months. 



From the time when the weather first grows cool in the autumn, 

 on until the cold weather has fairly set in, and the reign of ice and 

 snow commences, is the period during which the Alga? hunter 

 should search carefully all wet, dripping rocks, for specimens. 

 Amongst the stems of wet mosses — in dark, damp crevices, and 

 little grottos beneath shelving rocks — is the Algse harvest to be 

 reaped at this season. Nostocs, Palmellas, conjugating Desmids, 

 Sirosiphons, various unicellular Algas, then flourish in such 

 localities. My experience has been thatlate in the autumn ravines, 

 railroad cuttings, rocky river-banks, &c, reward time and labour 

 better than any other localities. 



The Vaucherias, which grow frequently on wet ground, as well 

 as submerged, fruit in the early spring and summer in this lati- 

 tude, and are therefore to be collected at such times, since they 

 are only worth preserving when in fruit. 



In regard to Algae which grow on trees, I have found but a 

 single species, and do not think they are at all abundant in this 

 latitude. Further south, they seem to be the most abundant forms. 



As to the preservation of Alga?, most of the submerged species 

 are spoiled by drying. Studies of them should always, when 

 practicable, be made whilst fresh. Circumstances, however, will 

 often prevent this, and I have found that they may be preserved 

 for a certain period, say three or four months, without very much 

 change, in a strong solution of acetate of alumina. 



An even better preservative, however, and one much more easily 

 obtained, is carbolic acid, for I have studied Desmids with great 

 satisfaction which had been preserved for five or six years in a 

 watery solution of this substance. In regard to the strength of 

 the solution, I have no fixed rule, always simply shaking up a 

 few drops of the acid with the water, until the latter is very de- 

 cidedly impregnated with it, as indicated by the senses of smell 

 and taste. 



