Timherlake — Swartn-Spores of Hydrodictyon. 493 



until the whole protoplast is divided into uninucleate bodies 

 whose mutual pressure gives to each a hexagonal shape. The 

 hexagonal bodies appear to be separated by light lines. This 

 appearance is caused, as Klebs rightly observes, by the two 

 limiting layers of protoplasm being pressed together. This is 

 the condition described by Strasburger and Artari as the earli- 

 est stage in the division of the cell. At no time, according to 

 Klebs, do the cleavage vacuoles cut through either the plasma 

 membrane (hautschicht) or the vacuolar membrane of the 

 motlier cell. Klebs thinks that the cleavage is never complete 

 but that the swarm spores always remain attached to one an- 

 other by thin strands of protoplasm, which only disappear after 

 the spores have come to rest and the new walls are formed 

 around the young Cells. 



From the fact that in many cells the number of nuclei is 

 greater than the number of swarm spores that could be formed 

 from the same cells, Klebs suggests that there must be a fusion 

 of the nuclei in such cases prior to the complertion of the 

 cleavage. The observations of Braun and others of the disap- 

 pearance of the pyrenoids prior to cleavage is confirmed by 

 Klebs. 



I have published elsewhere a brief resume of some of the main 

 facts described in the following pages. (28) The material 

 with which I have worked was collected in the vicinity of 

 Madison, Wisconsin, from small, slow flowing streams or in 

 protected portions of the lakes surrounding the city. The 

 plants were generally brought into the laboratory in large 

 quantities and placed in aquariiun jars in well lighted places. 

 No attempts were made to use special culture conditions for 

 the production of swarm spores but it was often found that 

 they Avere produced within a few days after the collection of 

 the material. This phenomenon, however, was by no means 

 constant and very frequently material was kept in the labora- 

 tory for many da^'s without showing any signs of spore for- 

 mation. Very often cultures growing under diverse condi- 

 tions of light and temperature would all be producing swarm- 

 spores at the same time. I have not succeeded in finding any 

 material producing sAvarmspores when collected, but in some 



