388 HARPER— ORGANIZATION, REPRODUCTION 



space. The spaces between two cells become flattened to thin bi- 

 convex lense-formed figures. This change of form is accompanied 

 by increased density of the cell content, which also becomes more 

 deeply green in color. It appears that the cells are accumulating 

 reserve storage products to be used in the reproductive period. 

 The distinction between this sort of growth and that at the earliest 

 period, when the cells were developing their long lobes and large 

 intercellular spaces, is obvious and parallels the distinction between 

 the periods of growth and of maturing with the accumulation of 

 reproductive reserves in adult many-celled plants and animals. 



Reproduction in P. asperum. 



Al. Braun ('51) reported De Bary's discovery of the gametes 

 of Pediastrum in 1851 and Askenasy ('88) has described their con- 

 jugation and shown the similarity of the life history to that of 

 Hydrodictyon. Askenasy ('88) shows fully that the final forma- 

 tion of the new colony is essentially the same process when it comes 

 from a zygospore through the polyeder stage and when it is formed 

 directly by asexual reproduction from a cell of a parent colony. 



The method of asexual reproduction in Pediastrum has been 

 correctly understood since the work of Meyen ('28), who saw the 

 escape of the swarmspores, their free motion and later their com- 

 bination to form the young colony and Nageli ('49) correctly con- 

 cluded that since the number of cells in a colony is regularly a 

 multiple of two the cells must have arisen by bipartition. To be 

 sure. Conn ('08) rather casually describes the swarmspores as con- 

 tinuing to divide after they have come to rest. Whether this state- 

 ment of Conn's is based on his own observations or is merely an 

 a priori guess at what seems to him probable is not clear. Nageli 

 ('49) in 1849 I'^'^d already convinced himself to the contrary. There 

 can be no question but that the process of cell multiplication is com- 

 pleted before the swarming period. 



I have photographed more or less successfully a large number 

 of colonies with mother cells at various stages of division. There 

 can be no question that here we have a process of successive biparti- 

 tion of a multinucleated sporeplasm. Smith ('16) has figured from 



