PROTOCOCCUS. 179 



or compact shaded earth, forming a pulverulent stratum. The 

 cells are more properly niacrospores or microspores. 



Such Protococcus forms occur, however, not only in the process 

 of development, but also in conditions of decay. Large masses 

 are sometimes observed, resulting from the dissolution of fila- 

 mentous algae. Have observed this process, particularly in Spiro- 

 gyra, how cell walls fall to pieces and waste away ; the cell con- 

 tents, Proococcws4ike, are set free for a longer existence and 

 possibly for an asexual mode of reproduction. Cienkowski, a 

 close observer, made similar observations on Cladophora, Ulotlirix, 

 Hydrodictyon, Botrydium, and others. 



As far as our present knowledge goes there is no appreciable 

 distinction between the macrospores or microspores of different 

 genera of Chlorophylous filamentous alga3, particularly in the early 

 stages, after separation from the maternal cells ; later changes 

 may and do occur. 



I repeat some of the thoughts already expressed in the Intro- 

 duction (v. p. xiii) about the life-history of various genera of 

 Fresh-water Alga3; they have an intermediate, or arrested 

 existence. In this stage they not only exist, but multiply very 

 rapidly. The unicellular forms, ( Protococcacece) under consid- 

 eration belong to this class, and are among the most common, 

 because some of them can be found everywhere and at all 

 seasons of the year ; they exist equally well during the scorch- 

 ing heat of Summer and the frigid cold of Midwinter, but the 

 multiplication of the cells may be arrested during the extremes 

 of temperature. Damp, warm weather is most favorable to 

 increase. They multiply, ordinarily, by cell division in one or 

 two directions, not only one or two or even ten times over, but 

 hundreds of times. One cell, in the course of ten days has pro- 

 duced a family of twice 600,000 cells, under my observation; 

 I say twice, because a single layer on the glass on which they 

 grew contained 600,000 cells by liberal calculation, but the 

 clusters had the cells more or less piled two or three fold. 



In this condition they may exist for months forming green 

 crusts on the trunks of trees, etc., as already indicated. Some 

 of these under favorable circumstances, preferring cool and wet 

 weather, suddenly develop into filamentous algre, the same as 

 those from which they originated. Every cell may not develop, 

 just as little as every seed from the pods of wild flowers, or the 

 ears of grasses, or the spores from the capsules of mosses or 

 other cryptogamous plants; how many millions of these are 

 grown to die unseen; few ever come to perfection. These 



