16 G. T. HARRIS ON THE COLLECTION AND 



skim them off the bottom with a spoon, collecting as little mud as 

 possible in doing so. On another occasion when crossing a boggy 

 field in East Devon, a small cup-like hollow was noticed filled with 

 bog water that had a greenish appearance ; on filling a 3 in. by 

 1 in. tube with the water the colour was found to be due to 

 Euastrum oblongum in such prodigious numbers as almost to 

 allow of the term " desmid soup " being applied to the gathering. 

 These are the " pure gatherings " the authorities refer to. My 

 fate, however, has usually been to meet them so closely associ- 

 ated with their environment that the purity of the gathering from 

 a mounter's point of view has not confirmed the appropriateness 

 of the term. It is, of course, easy to understand these congested 

 associations of individuals of one species by reflecting that when 

 conditions are favourable, and division is actively taking place, 

 concentration must result unless the water has sufficient motion 

 to distribute the plants. 



Wherever a thin growth of conferva spreads itself on stones in 

 slow-running streams, or over the surface of submerged woodwork, 

 desmids may be expected to occur, and the film should be care- 

 fully removed and bottled. The flocculent matter that collects 

 around the stems of aquatic plants in ponds and the back-waters 

 of streams may be collected by Prof. West's trick of clipping 

 the stem below the surface of the water between the closed fingers 

 and making of the hollowed hand a cup in which the flocculent 

 matter is collected by drawing the hand upwards. Masses of 

 Spirogyra may be lifted out of the water, drained, wrapped in 

 waterproof paper and deposited in a vasculum ; desmids will 

 generally be found entangled among their threads and may be re- 

 moved at home. Mosses from wet tree trunks are best separated 

 and the stems washed vigorously in a dish, when the desmids, if 

 present, will be washed away from the moss. Generally speaking, 

 moss habitats are not prolific hunting-grounds, the species 

 occurring amongst them being principally those of the genus 

 Mesotaenium. Swift mountain streams at first sight do not strike 

 one as likely hunting-grounds, but the confervae attached to 

 the rocks often contain many good species. My introduction to 

 the comparatively rare Closterium didymotocum took place at the 

 head waters of the River Teign on Dartmoor, where it occurred 



