15 



THE COLLECTION AND PRESERVATION OF DESMIDS. 



By G. T. Harris. 



{Read January 25th, 1916.) 

 . Communicated by James Burton. 



The publication by the Ray Society of Prof. West's Monograph 

 of the British Desmidiaceae has induced so many microscopists 

 to concentrate their attention on this beautiful group that I feel 

 no apology is needed for describing methods that have proved 

 advantageous in my hands, both in collecting the material and 

 in dealing with it when collected. I am aware that the litera- 

 ture dealing with the collection and preservation of desmids is 

 not inconsiderable, and that formulae for mounting media have 

 been given with a generosity only equalled by their shortcomings ; 

 yet the hope that one may perhaps contribute some method that 

 shall prove more or less useful overcomes the reluctance to add 

 yet further to the burden of contributed matter on the subject. 

 The complaint not infrequently made by the uninitiated of 

 their lack of success in obtaining desmids may be due more to 

 their method of collecting than to the absence of desmids. The 

 orthodox ring-net will, of course, collect a considerable number 

 of unattached specimens, but the bulk of desmids are usually 

 attached by their gelatinous secretion to objects that are more or 

 less stationary, hence the ring-net misses these unless it happens 

 to brush them off and they find their way into it. The habitats 

 of desmids also are probably of much greater diversity than the 

 average microscopist realises, and vary from a roadside ditch 

 with merely a few inches depth of water in it to a moorland tarn ; 

 from the wet, moss-grown trunk of a tree to the dripping face 

 of some perpendicular rock. Last spring in a roadside ditch near 

 Sidmouth, with barely a quarter of an inch depth of water, was 

 a perfect film formed of individuals of Closterium Ehrenbergii, in 

 extremely fine condition. The only way to collect them was to 



