The Scottish Naturalist. 157 



have never seen anything like the processes described by De Bary ; 

 but I would be more inclined to hold, with Hofmeister, that the 

 various transformations take place in the zygospore itself, and not 

 that portions of the contents escape separately, division taking place 

 afterwards. 



A third supposed mode of increase is by means of zoospores. 

 These were detected in one species, Docidium Uhrenbergii, by my 

 valued friend, Mr. Archer of Dublin, and published by him in the 

 Natural History Review for July, i860. He describes them as being 

 comparable in appearance and mode of formation to the Zoospores 

 in Cladopkora, where they undoubtedly propagate the plant, and 

 form young colonies in abundance. He observed them in the month 

 of September. The curious thing is that no one seems to have ob- 

 served them since. Probably they are formed late in the season 

 when these plants are seldom looked for, and they may therefore be 

 more common than is generally supposed ; at the same time, I am 

 bound to state that, though I have collected Desmids at all seasons, 

 I have never seen the zoospores. 



The power of movement in Desmids is an interesting point in their 

 history. Probably all their movements depend on the influence of 

 light. It has long been known that if they are covered with mud, 

 and exposed to the light, they will quickly make their way to the 

 surface, which affords the opportunity of securing clean gatherings 

 not otherwise easily made. A peculiarity of this process is a tendency 

 to turn the longer axis towards the light, with the younger half of the 

 cell next it. Tetmemorm granulatus often shows a forward movement, 

 and some species of Closterium, resting themselves on their tips, sway 

 backwards and forwards for a considerable time. The cause of these 

 movements is not well understood, or rather is not understood at all. 

 Another peculiar state of matters is equally obscure, that namely in 

 which the cell contents become changed iuto a mass of granules 

 moving with great rapidity. This state is best seen two or three days 

 after they have been gathered. It is quite a different state from the 

 movements of the granules seen near the extremities of Closteria, 

 and of other genera, which are normal in these plants. 



Desmids are to be found most abundantly, in comparatively small, 

 shallow, permanent pools of clear water in open situations. They 

 nestle among the leaves of such plants as Myiriophyllum, Ltricularia, 

 Chara, Sphagnum, &c, or they attach themselves to submerged stems 

 of grasses and other plants. Many interesting species occur in tufts 

 of moss on wet rocks. Others occur abundantly in rapid streams, 

 attac hed to tufts of Fontinalis, and other mosses. One species has 



