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 plankton22 The water may become 
turbid and quite yellowish-green through the swarming 
myriadsjof alge. A pin’s head dipped in such a lake 
may bring up three hundred specimens.* 
In examining such plankton algz 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 alge, 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 larve of insects and of small crustaceans 
to whom these spiny processes would be formidable ! 
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 Desmidiacez if he wishes to appreciate these 
points, 
* Cooke’s British Freshwater Algae. 
40 
