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 

 o'lass vessel with a film of brio-ht o-reen 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 



