GREEN SLIME. 



Protococcus viridis Ag. 



PRELIMINARY. 



THE plant selected to illustrate the simplest phase'of 

 vegetable life is found in all parts of the United 

 States, and even throughout the world. It grows 

 upon the surface of various objects, being often so 

 abundant as to give them a conspicuous green color, 

 especially upon the north side of old fences, barns, 

 and the trunks of trees, becoming more noticeable 

 after a few days of damp weather. There are several 

 other closely related species that may be used, in 

 fact almost any unicellular green plant will answer, 

 but this is the one most likely to be gathered. Some 

 kinds of unicellular plants, like Gl&ocapsa, have a 

 sheath or envelope outside the cell proper, not found 

 in Protococcus, a fact to be borne in mind by the 

 student if such plants are used. Pieces of bark or 

 wood bearing the alga may be kept dry for use, and 

 will give a fresh appearance when moistened with 

 water, and even retain vitality for a year or two. 



It is quite likely that the plants known under the 

 name of Protococcus are but early forms of some more 

 complex algae 1 , but, however this may be, they serve 



1 Bessey, Botany, p. 219 ; Wood, Fresh-Water Algae of North 

 America, p. 10 ; Sachs, Text-Book of Botany, 2nd Eng. ed., p. 248 ; 

 Cienkowski, Bot. Zeit. 1876, p. 17. 



