ON SCOTTISH DESMIDIE^: 109 



from the labour involved in rewriting and rearranging the 

 whole. 



" Suitable localities " have been spoken of. It may be 

 asked, What are suitable localities ? They are of various 

 kinds. Amongst the best are comparatively small perman- 

 ent pools of clear water, a few square feet or yards in extent, 

 with floating SpJiagnuin round their margins. The Desmids 

 nestle among the SpJiagnmn leaves, and have to be squeezed 

 out. Such localities often yield large numbers of species. 

 In similar pools Myriophyllinn, Utricularia, Chara, and 

 Nitella will always be worth treating in the same way as 

 Sphagnum. Occasionally the Desmids form small, pale, 

 yellowish-green films on the mud at the bottom of pools, and 

 can be taken up with a little care. It requires a little more 

 care to strip the submerged stems of grasses, etc., between 

 one's fingers, and to secure the stripped materials ; but this 

 process often yields very interesting results. Another very 

 suitable locality is in tufts of moss growing on rocks and 

 stones which are kept constantly moist. Many of our rarest 

 and most beautiful species are found on such spots, from 

 cliffs by the sea to high up on our mountains. 



And here I must be permitted to enter a protest against 

 a practice among writers on Desmids, more particularly in 

 recent years. I refer to the multiplication of so-called var- 

 ieties. Some species seem to have been specially fixed on 

 for the application of this process. Take the case of Cos- 

 inariuin MenegJiinii, Breb., for instance. This tiny species 

 has been so covered over with these vars. that it runs a risk 

 of being crushed out of existence altogether. And yet the 

 original form of Brebisson, as figured by Ralfs, and its zygo- 

 spore figured by Mrs. Thomas in the " Quarterly Microscop- 

 ical Journal," vol. iii., is surely a distinct enough species. But 

 so, it seems to me, is De Bary's form, and so are several 

 others. Now, if these forms maintain their individuality, 

 and that they do so is undoubted, I fail to see the utility of 

 crowding them together as varieties. Why not make species 

 of them at once ? The time will no doubt come when 

 species will be largely reduced, but it has not come yet ; 

 neither will it be accelerated by the indiscriminate manu- 

 facture of varieties, and still less by what is worse, varieties 



