6 MINUTE MARVELS OF NATURE 



Every moderately clear pool or ditch will provide 

 examples of these interesting plants, and they 

 especially abound in ponds which lie in exposed 

 and bleak situations. The species in the illustra- 

 tion is characterised by its crescent-like form. 

 Each cell is free and able to move about in the 

 water by a curious, feeble movement, and if kept 

 in a glass vessel they all move slowly to the side 

 next to the light and congregate there. For a 

 period of over twelve months I kept a large 

 quantity of these desmids propagating in a 

 common glass jar, having accidentally gathered 

 a few attached to some of the common duckweed 

 which floats on ponds. 



Desmids, like other green plants, evolve oxygen 

 in sunlight ; and so, together with the duckweed, 

 which also multiplied in the glass jar, the water 

 was kept fairly pure, and the desmids increased 

 at such a rate as to completely line the sides of the 

 glass vessel with a film of bright green colour. 



A desmid cell possesses a thin outer coating or 

 cell-wall, sometimes adorned with spiny projec- 

 tions or markings. Surrounding this, a trans- 

 parent film of gelatinous matter is recognisable, 

 although sometimes only by its preventing the 

 cell-wall from touching external objects. Inside 

 the cell-wall proper is a layer of colourless proto- 

 plasm, which encloses the mass of green-coloured 



