24 G. T. HARRIS ON THE COLLECTION AND 



keep well. The fine species Xanthidium armatum turns rather 

 yellow-green when old cells are mounted. 



On one point I have no doubt whatever, which is, that it is of 

 very considerable importance to store the desmids in the water in 

 which they are found growing, and I am quite prepared to admit 

 that the colour preservation in my specimens may be due as 

 much to this fact as to the particular preserving agent used. Bogs 

 are usually massed with sphagnum of one species and another, 

 and it has been stated that the sphagnol present in them is a 

 powerful antiseptic. If this is so, and if sphagnol is soluble in 

 water, it might be possible to dispense with a preserving agent 

 and rely on bog water pure and simple. However, I do not advise 

 anyone risking their material by relying altogether on the anti- 

 septic properties of " sphagnol," as I am quite certain that the 

 aquatic life generally captured with the desmids would have the 

 last word. In support of the sphagnol theory, however, it is a fact 

 that the zone of decayed matter in a bog is in a very different 

 condition from the floor of a weed-grown pond. It is unpleasant 

 of course to plunge into a bog over one's knees and emerge coated 

 with brown slime, but at least one is spared the unmistakable 

 bouquet that such an experience in a pond would entail. 



The fact that some individuals in the same gathering and 

 preservative retain their colour, while the colour of others has 

 deteriorated, is due most likely to the age of the plant, and prob- 

 ably also to some pathological condition of the cell. Naturally, 

 the most vigorous plants would be the better preserved, and it 

 only remains when mounting to pick out those that seem to be 

 deeper in colour than the others. This is very noticeable in 

 Micr aster ias rotata, where some individuals may be deep green and 

 congested with chlorophyll granules, while others are extremely 

 pale and semi-transparent — in other words, probably decaying 

 plants. 



The fluid in which the desmids are mounted is sipiply the bog 

 water to which the preservative was added at the bog side. Usually 

 when filling up the tubes and bottles a certain amount of the fluid 

 is superfluous. On reaching home this supernatant clear portion 

 in each bottle is laid under contribution to accumulate a stock 

 solution, which is filtered and forms the mounting fluid. It will 



