CHAPTER XIV. 

 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 (yeast, bacteria, diatoms, desmids, etc.) or discolorations 

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

 tococcus, Glwocapsa, etc.). 



Under the term Protococcus (rrpoTOS, first, KOKKO;, bt-rrt/) 

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

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

 ities in classification, 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-greea 

 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 

 tides detached consist of rounded yellowish-green cells occurrii 

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



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