CHAPTER XIY. 



UNICELLULAR PLANTS. 



A. Protococcus. 



(Protococcus, Pleurococcus, Chlorococcus, Hcematococcus, etc.} 



UNICELLULAR plants, like unicellular animals, are very com- 

 mon, although as individuals mostly invisible on account of their 

 microscopic size. In the mass, however, they are often visible 

 either as suspended or floating matter, causing ' ' turbidity ' in 

 liquids (i/east, bacteria, diatoms, desmids, etc.) or discolorations 

 011 tree-trunks, earth, stones, roofs, and flower-pots. (Pro- 

 tococcus, Glffiocapsa, etc.). 



Under the term Protococcus (npoTos, first, KOKKO?, berry) 

 we may for our present purposes include a number of the simplest 

 spherical forms, generally green in color and of uncertain affin- 

 ities in classifl cation, but very similar in structure, living for the 

 most part in quiet waters or on moist earth, stones, tree-trunks, 

 or old roofs, or in water-butts, roof -gutters, and the like. 

 Sometimes the color which they exhibit is yellowish-green, 

 sometimes bluish-green, and sometimes, though less often, reddish, 

 according to the species. 



One of the commonest and most conspicuous is a species 

 often seen on the shady side of old tree-trunks where, when 

 abundant, it forms a greenish dust-like coating or discoloration, 

 scarcely visible when dry but becoming a rich bright green dur- 

 ing prolonged rains or after warm showers. If pieces of bark 

 covered with this form of Protococcus are moistened, the green- 

 ish coating may be observed at any time. It is granular in tex- 

 ture and after moistening is easily loosened by a camel' s-hair 

 brush. 



Morphology. Microscopical examination shows that the par- 

 ticles detached consist of rounded yellowish-green cells occurring 

 either singly or in groups of two, three, four, or even more. 



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