STUDIES OF SPORE-PLANTS 



247 



237. Pleurococcus. A green coating or stain which is 

 often seen on the shaded (usually north) side of tree-trunks, 

 unpainted walls, etc., will be found upon microscopic ex- 

 amination to be composed of masses of one-celled plants, 

 often arranged in groups of two, four, or more cells (Fig. 74). 

 This grouping is the result of repeated cell-division. Each 

 cell has protoplasm, nucleus, chlorophyll-bodies, and cell- 

 wall. Having chlorophyll, they 



are able to make carbohydrates 

 from carbon dioxide and water. 

 Particles of dust lodged on the 

 wood on which they grow prob- 

 ably supply the necessary ma- 

 terials which higher plants 

 absorb from the soil. Abun- 

 dance of water favors growth, 

 and they appear a brighter 

 green during rainy weather. 



238. Sphaerella. Red stains 

 are often seen in hollows in 

 rocks, in empty urns in ceme- 

 teries, in roof-gutters, and in 



similar places where dust may collect and where temporary 

 pools of water may be formed by rains. If water is present 

 in such hollows, it may be reddish or greenish in color. 

 Collect some of the dry dust, decayed leaves, etc., from such 

 places during the autumn, and keep dry until wanted for 

 study. Then place some of the dry material in water, and 

 expose to light for several days. Examine with the micro- 

 scope some of the dry material mounted in a drop of water 

 and observe spherical cells with red contents (protoplasm 

 plus a coloring matter), and with thick cell-walls. This is 

 called the " resting stage " of the Sphaerella plant. By special 

 methods it is possible to extract the color, and demonstrate 

 a nucleus near the center. It is evidently a one-celled plant. 



FIG. 74. Pleurococcus. a, one cell; 

 6, two cells formed by division of 

 a; c, three cells by division of one 

 of two cells in b; d, four cells; 

 cw, cell-wall; n, nucleus; cell- 

 body between nucleus and cell- 

 wall contains chlorophyll. (From 

 Sedgwick and Wilson.) 



