626 MINNESOTA BOTANICAL STUDIES. 



was wide and gelatinous. Though piled up together, the cells 

 for the most part were disconnected. Sometimes two or three 

 were connected after the manner of Gongrosira cells (PI. 

 XXXIV, fig. 2). Some entire heaps had secreted gelatinous walls 

 and already had the appearance of a plate. Thus the first con- 

 dition merges into the second (2) first by the development of the 

 individual membrane into a mucilaginous substance, second by 

 the coalescence of this substance with that of the neighboring 

 cells, thus forming a continuous layer of gelatine common to 

 the whole group of cells. In this way cells which were lying 

 close together become driven apart a slight distance from each 

 other and have the appearance of being suspended in the gela- 

 tine. Their aspect is that of Tetraspora cells except that they 

 are not arranged in twos or fours. In this stage of the process 

 they are more nearly spherical in form and are fresher looking 

 than at a later period. In general nearly one-half of each cell 

 is almost colorless. 



Later these cells lose their fresh color and become dull 

 and dead looking. The gelatinous layer between them be- 

 comes contracted into thin leathery division walls, common 

 to the cells on either side. It is believed that this condition 

 of things precedes the development of microzoospores. At 

 any rate, at the end of three weeks the sides of the glass tank 

 containing pebbles "6" and "7" had acquired a dull green color 

 which was proved to be caused by the presence of these plates 

 with the appearance just explained. They were dividing into 

 microzoospores, to the number of 4-8 in a cell (PI. XXXIV, fig. 

 4). This was the first instance of cells in plates developing 

 zoospores, though a most exhaustive search had been made 

 for the purpose of finding this condition. The mother-cells 

 in the figure given, were 12-15 mic. in diameter in the main; 

 some were very much smaller — 4-mic. in diameter. Those 

 from which the zoospores had not yet escaped were generally 

 spherical and swollen. The empty ones were more angular 

 and collapsed. Around the edges of the large plates and also 

 from cells in the interior, there grew out branches of the 

 Pilinia type the cells of which varied from 4-10 mic. in diame- 

 ter. These filaments did not stand upright, as is usual, but 

 occupied the same plane as the plate. A portion of a plate is 

 shown ( PI. XXXIV, fig. 4) in which appear a vegetative per- 

 ipheral plate cell with its large central pyrenoid, embedded in the 

 chlorophyll and granule-bearing protoplasm. From its outer 

 side extends a filament in all respects like an ordinary Pilinia 



