Seaweeds and Leaf-green 



early and some late in the spring, others in summer, and 

 yet others late in autumn. This is also specially true of 

 the fresh-water plankton.22 The water may become 

 turbid and quite yellowish-green through the swarming 

 myriads,- of algae. A pin's head dipped in such a lake 

 may bring up three hundred specimens.''^ 



In examining such plankton algae one is often almost 

 startled by the large flaring-green and oddly shaped 

 desmids which float across the field of the microscope. 

 These also are one-cell algae, and are of the strangest 

 and most curious designs. Some are nearly circular, 

 but slashed and cut so as to look more like the frost- 

 figures on a window-pane than anything else. Some 

 are thin crescents, or they may be triangular or rosettes, 

 but generally of the same flaunting vivid green colour. 



Many of them are provided with projecting harpoon- 

 like arms, often with distinct hooks at the tip. 



One would think on looking at these weird projections 

 that here one has at last an example, so often looked 

 for, of something which cannot possibly be of any service 

 to the plant. 



But this defensive armour of spiny projections has 

 most probably been acquired as a means of resisting the 

 attacks of their enemies. The amoeba, which is nothing 

 but a small piece of living protoplasm, cannot so well 

 wrap its slimy body round such a desmid. There are 

 also aquatic larvae of insects and of small crustaceans 

 to whom these spiny processes would be formidable 1 

 The desmids on wet rocks and such places as are not 

 haunted by such enemies are usually without these 

 spines. The reader is strongly advised to look through 

 the illustrations in Mr. West's splendid monograph of 

 the British Desmidiaceae if he wishes to appreciate these 

 points. 



* Cooke's British Freshwater Alga. 

 40 



