XIV FKESH-WATER ALG.E OF THE UNITED STATES. 



In Fresh- water Algae, perhaps more than in any other class of 

 cryptogamous plants, is this peculiar, arrested character of plant- 

 life observed. It is found everywhere either in immediate con- 

 nection with or independent of the more fully developed plants. 

 Usually it presents itself in unicellular forms, embracing the 

 forms of such old genera as Protococcus, Pleurococcus, Chloro- 

 coccum, and others among the Chlorophycese, and Gloeocapsa, 

 Aphanocapsa, Microcystis and many others among the Cyanophy- 

 cese. The cells divide, and redivide many times over. To say 

 that one single spore, or cell, will produce thousands of its own 

 kind in the course of a few days, is no exaggeration, yet all of 

 these, or nearly all, are merely single cells, serving apparently 

 no purpose except to form a bed or stratum from which in due 

 time, when the particular requirement of temperature and 

 moisture are supplied, a plant, or plants, will develop, repro- 

 ducing the original filamentous type. 



When we consider that in all vegetation the process of cell 

 multiplication takes place by division of cells, that this is the 

 process of growth in every stem and leaf, but differing ; in 

 these the cells remain united to increase the size, whereas in 

 alga) the cells separate the process of multiplication and growth 

 of the so-called unicellular forms is not so altogether singular. 

 As in the growth of a leaf hundreds and even thousands of cells 

 are evolved before a leaf is fully matured, so in algse many 

 thousands of cells are produced before the true plant is developed. 

 There is at least an analogy between the two in principle of 

 development. 



P. H. Dudley, in a recent paper read before the New York 

 Microscopical Society (see document of said Society Vol. II, No. 

 I. p. 9), on Protococcus viridis, takes a philosophic view of this 

 condition of plant-life. A few lines may be transcribed : i i As 

 humble as our plant may seem from its classification, modern 

 science is still unable to solve its mysteries ; it is one of the 

 great manufacturing chemists among plants, converting crude 

 materials into combinations which, upon decay, may be taken 

 up by higher vegetation. Spread out upon trees and rocks, its 

 gelatinous substance is ready to catch and imbed the floating 

 dust and inorganic matter brought to it by the wind, some of 

 which will be converted and used. The air also brings great 

 carboys of carbon di- oxide and exchanges them for oxygen. 

 Fumes of sulphuric, sulphurous, nitric and nitrous acids, and 

 also ammonia come to be combined ; the rain brings chlorides 

 and other chemicals to be utilized. Each of the individual cells 

 of Protococcus viridis, only measuring from two to ten Micro- 



