Tilden: pilinia and stigeoclonium. 613 



It has been impossible to do more with this problem while at 

 such a distance from the spring. It can only be said that the 

 conditions present in the spring seem to meet the needs of the 

 Pilinia stage and that only. When removed from those condi- 

 tions the plant transforms itself into Stigeoclonium and that 

 in turn changes into the Palmelloid stage. 



2. Stigeoclonium Stage: Fifteen days after the Pilinia plant 

 had been under cultivation, a small mass of waving filaments 

 about 3 mm. long was observed on pebble "5." Heretofore, 

 though examined often, nothing but the layer of dull looking 

 plate cells had been observed on this pebble. These filaments 

 were found to proceed from Pilinia plate cells and a thorough 

 investigation of them proved beyond a doubt that the plant 

 was a Stigeoclonium. 



A day or two later material taken from, pebble "3" showed 

 under the low power, a small spherical Pilinia thallus out of 

 which grew long filaments of the Stigeoclonium type. One of 

 the longest of these, measured 1125 mic. in the portion that 

 projected beyond the general mass. Of this length 625 mic. 

 belonged to the bristle, leaving 500 mic. in the vegetative por- 

 tion. The upper vegetative cells were 9-10 mic. in diameter, 

 and from 1£ to two times as long. They were entirely filled 

 with protoplasm and chlorophyll. Each contained from two to 

 four pyrenoids and some smaller granules. The filaments with 

 one exception were unbranched. Near the end of this filament a 

 short branch was given off. All the filaments were evidently 

 about to form zoospores. 



Subsequently, much of the Pilinia material developed into 

 the Stigeoclonium stage. 



The Stigeoclonium tb alius showed on an average, a length of 

 30-35 mm. It is light green in color and so very delicate in ap- 

 pearance, that one finds it difficult to recognize its presence in 

 the water. 



A single tuft or mature thallus when examined as a whole 

 (PI. XXXIII. fig. 1), shows at the base, short Pilinia shoots radia- 

 ting from the cushion of plate cells. These are relatively 

 few, the majority of them being produced into the long Stigeo- 

 clonium threads. These main filaments are simple for some 

 distance from the base and consist of articulations 9-15 mic. 

 in diameter, with a length 1^-8 times as much. At length 

 groups of short, somewhat globose cells begin to alternate 

 with the ordinary long ones, and these are the cells which bear 



