THE VICTORIAN NATURALIST. 33 



filamentous alga with axile chloroplasts, and Hyalotheca and 

 Desmidium in long bands, containing scores of small compact 

 cells something like species of Cosmarium when detached ; and, 

 again, see the normally independent Cosmarium, which has 

 grown by vegetative cell division until one plant has given rise to 

 four which remain attached by their apices to form a moniliform 

 band. These bands are all more or less fragile, in Spondylosium 

 particularly so, and break up into single cells, though, as a rule, 

 the longer the cells the more readily is dissociation affected by 

 mechanical and other means. 



A series of microscopic exhibits show various stages in the 

 asexual multiplication. For this purpose I have chosen a plant 

 of the genus Micrasterias, and another of the genus Cosmarium. 

 These show first the matured plant and various stages in the 

 separation of the semi-cells, to allow of the interposition of new 

 matter, which at first is almost colourless. Gradually this new 

 matter is seen to pinch in the middle, and the halves between 

 this pinched-in median line and the old semi-cells to assume a 

 shape somewhat approaching the latter in appearance, and 

 finally to acquire that shape exactly. The two new semi-cells 

 thus formed between the old ones having, in growing, thrust the 

 latter apart to the extent of a Desmid's length, we have now 

 two plants, the apices of their newly-formed semi-cells touching, 

 and the older semi-cells outermost. Another exhibit shows two 

 such newly-developed plants just after separation. The chief 

 difference between the semi-cells of a new plant is that the 

 ornamentation of the cell wall is not fully matured at time of 

 separation, e.g., the exhibited Closterium malinvernianum, De 

 Not, has one half of the cell wall distinctly striated, while the 

 other is smooth. The striations on the old semi-cell wall dis- 

 tinguish this species from Closteriiun ehrenhergii, Menegh., also 

 exhibited, and from the same lagoon at Heidelberg. It is an 

 instance of the importance of the cell wall ornamentation, 

 indispensable in many cases when diagnosing. 



The multiplication of Desmids by means of zygospores has 

 been known to science for many years, but the details of the 

 process are still under discussion. I am exhibiting a plant, Tet- 

 viemorifs brcbissonii, Menegh., in several conditions, viz. : — (a) 

 the simple in.dividual ; (6) a newly formed smooth-walled spherical 

 zygospore, together with the empty cell-cases, which have parted 

 at tlie suture which marked the middle of the plant in the 

 constricted area, and which, in their empty state, permit the cell 

 wall ornamentation to be clearly seen ; (c) a group of eight new 

 plants, which have been freed from the product of a single 

 zygospore. This Desmid is from a swamp near Brighton. 



The movements of Desmids are of three kinds, though all three 

 may not be seen in all genera. First there is the movement 



