Tilden: pilinia and stigeoclonium. 623 



were visible except the long bristles radiating out in every 

 direction. Some of them were 100 mic. or thereabouts in 

 length. ^ 



Carefully removing one of the thalli with a scalpel and 

 camel's hair brush, under the same power of the microscope it 

 was found to consist of a plate, the upper surface of which 

 (that is the surface exposed to the water) was convex, while the 

 lower side (that resting on the glass) was concave. Prom the 

 convex surface the upright filaments stood out in all directions. 

 From many of them very long bristles were produced. 



The thalli occurred on all sides of the glass dish, but not at 

 the surface of the water as those in the first tank did. They 

 were scattered on all portions of the vessel walls from the bot- 

 tom to the surface of the water. 



The high power showed the following points: The upright 

 filaments at this stage were in the neighborhood of 37.5-45 mic. 

 in length and 5 mic. in diameter. 



The cells were in general 9-12 mic. in length. They were 

 densely filled with protoplasm, were bright, vegetative green in 

 color, and contained a distinct pyrenoid and some granules. 

 The cells appeared to be about to form zoospores. Some were in 

 process of division. The basal cells were 10 mic. in diameter. 



A view is given of a section of plate cells in diagram (PI. 

 XXXV, fig. 7) from the under surface. It shows the position 

 of a single branch (fig. 8) as it lies in the plate. 



The sides of the tank containing pebbles "3 " and "4" (the 

 material being in the Pilinia stage) were dotted over with small 

 solitary thalli with the same appearance as those which covered 

 pebble " 2 " which was placed in the herbarium. 



Transformation into the Palmella Stage. — The presence 

 of Palmella-like cells has been very noticeable in nearly every 

 mount prepared from the Pennsylvania material. Little notice 

 was taken of them at first, as it was supposed they had nothing 

 to do with the Pilinia. Later, however, cells exactly corres- 

 ponding to them in size, shape, and general appearance were 

 observed to be connected with the Pilinia plant. The first in- 

 stance of the kind was seen in a detached branch of Pilinia 

 (PI. XXXIII, fig. 11). One branchlet, instead of being 

 made up of the ordinary cylindrical cells was composed 

 of ten globular, thick-walled, Palmella-like cells. One 

 was in process of division into halves. The cells appeared 

 to be surrounded by no membrane common to them all, but 



