280 



THE MICROSCOPE 



Desmidiacece. — The once disputed question relating to 

 the vegetable nature of these cells received much valuable 

 elucidation from Mr. Ralfs, who gave to the world 



tha 



Fig. 152. 



I, Euastrum oblongum. 2, Micrasterias rotata. 3, Desmidium quadrangulatum. 



4, Didymoprium Grevillii. 



results of his laborious researches in his excellent work on 

 The British Desmidiece, published in 1848; and the con- 

 elusions arrived at by this painstaking author have been 

 generally accepted by men of science. The interest which 

 has so long attached to this topic will warrant us in 

 devoting some space to its consideration ; and we avail our- 

 selves for that purpose of Mr. Ralfs' labours, with a 

 recommendation to those of our readers who would 

 wish to familiarise themselves more completely with this 

 peculiar species, to consult the pages of the book above 

 referred to. 



Desmidiacece are grass-green in colour, surrounded by a 

 transparent structureless membrane, a few only having 

 their integuments coloured ; they are all inhabitants of 

 fresh water. Their most obvious peculiarities are the 

 beauty and variety of their forms and their external mark- 

 ings and appendages ; but their most distinctive character 

 is their evident division into two or more segments. Each 

 cell or joint in the Desmidiacece generally consist of two 

 symmetrical valves or segments ; and the suture or line of 

 junction is in general well marked. The multiplication of 

 the cells by repeated transverse division is full of interest, 



