Methods of Peeservation 141 



Methods of Preservation 



Where cell characters are among the chief requisites for the 

 determination of species, as is the case with many of these plants, 

 specimens preserved on paper, according to the usual method with 

 seaweeds, are, to say the least, extremely unsatisfactory. Indeed, 

 one is sometimes tempted to discard such methods altogether. 

 Nevertheless, this method is, in certain respects, of considerable 

 value, and should be generally, though not exclusively employed ; 

 paper or mica mounts are most convenient for the herbarium to 

 show distribution and form in the mass ; furthermore, they furnish 

 a record which is likely to be permanent, while slide mounts are 

 more liable to deterioration or accidental injury. 



For purposes of accurate study, however, and for convenience 

 of comparison of a large number of specimens, it is necessary to 

 have material fixed and mounted on slides, or at least preserved 

 in bottles. Of the more elaborate methods, we have attained 

 greatest success by fixation in Flemming's stronger solution, fol- 

 lowed by staining in iron haematoxylin, with the addition of a 

 light counter-stain of Congo red. Great care is necessary to pre- 

 vent plasmolysis and distortion.* This method requires too much 

 time if one desires a large series of one species for comparative 

 study. 



The following simple method has proved of great service ; 

 enough material for two or three mounts is dropped into a small 

 bottle of Flemming's stronger solution for a few seconds or 

 moments (the length of time varying with the delicacy of the 

 species), then rinsed hastily, arranged on slides, and covered with 

 a few drops of two to five per cent, solution of chromic alum ; the 

 cover-glass is laid on, the superfluous fluid removed with filter or 

 blotting paper, and the mount sealed with colorless marine glue. 

 Preparations made in this manner are somewhat liable to deteri- 

 oration because of defective sealing, but enough mounts may 



* The most useful discussion of this and similar methods is to be found in the articles 

 by C. J. Chamberlain, Journ. Applied Mic. i: 156. 1898; 2: 506,543. 1899, and 

 in the more elaborate work of F. Pfeiffer von Wellheim, Zur Praparation der Susswas- 

 seralgen. Jahrb. wiss. Bot. 26 : 674-732. 1894, and Beitrage zur Fixirung und 

 Praparation der Siisswasseralgen. Oesterr. Bot. Zeit. 48 : 53—59, 99-105. 1898. 

 (Translation in Bull. Soc. Belg. de Mic. 24: 22-103. 1898.) See also a note by- 

 Charles Thom, Bot. Gaz. 24 : 273. 1897. 



