Tilden: pilinia and stigeoclonium. 607 



Rabenhorst (I) gives a figure of Pilinia rimosa, which though 

 it does not afford a very definite idea of the plant corresponds 

 in essential points to the Pilinia stage of Stigeo clonium. It 

 shows basal cells and short upright filaments which branch in 

 a simple manner towards the apex. 



The plate cells, or basal cells of the filament, originally 

 spherical in form, like all algal cells which unite in plates, 

 soon become angular in outline. Their diameter is in the 

 neighborhood of 12 mic. When the plant is in a healthy con- 

 dition they are nearly filled with a vegetative green coloring 

 matter. Each one contains a large and distinct pyrenoid 

 sometimes occupying as much as one-third the diameter of the 

 cell. Near this there is a clear, colorless space, depending 

 it would seem for its size and distinctness, upon the age and 

 condition of the cell. It is scarcely noticeable in young plants 

 but becomes larger and more apparent as the cell matures. 

 In general several granules of different sizes are present. 



A somewhat interesting point is the occurrence of etiolated 

 cells in close proximity to cells in apparently flourishing con- 

 dition. In the material taken from pebble "3," after it had 

 existed ten days out of its natural abode, the basal cells in small 

 fragments of the plant, were sometimes all colorless, some- 

 times all chlorophyll-bearing, and sometimes the two states 

 occurred together. The upright filaments growing from these 

 frequently had their lower cells perfectly colorless, while the 

 upper ones were chlorophyll-bearing in the usual manner. 

 Very often a row of basal cells was entirely colorless, while all 

 the cells in the filaments arising from them were chlorophyll 

 bearing and appeared healthy in all respects. 



The material when taken directly from the spring has always 

 shown the Pilinia state. In the upright filaments of this the 

 cells are long and cylindrical The branching is sometimes 

 dichotomous like that of aChsetophora (PI. XXXII, fig. 2 and 3), 

 or in other cases the branches given off are few and simple like 

 those of Stigeoclonium (PL XXXII, fig. 1). Also the filaments 

 may attain quite a height without branching at all or they may be 

 profusely branched throughout. The lower cells are from 5-7.5 

 mic. in width, with a length of 2£ to 3 times as much. The 

 upper cells are 7.5 mic. in diameter and 2^ times as long. 



In the lower cells of the filament a protoplasmic mass con- 

 taining the chlorophyll grains and starch granules occupies 

 approximately the central third of the cell (PI. XXXII, fig. 3). 

 The two ends are colorless and apparently empty. The propor- 



