628 MINNESOTA BOTANICAL STUDIES 



cells. The spores agree in size. They are possessed of only two 

 cilia (PI. XXXIV, fig. 5). In several mounts a zygote was 

 seen. The first one noticed contained two distinct pigment 

 spots and was bilobed at the lower end, showing conclusively 

 that it was a case of fusion (PI. XXXIV, fig. 6 a). The number 

 of cilia could not be determined but was supposed to be four. In 

 another mount in which many of the plate cells were empty, a 

 spore with two eyespots was seen (fig. 6 b) . Near by was an 

 elongated body, its shape giving it the appearance of being 

 made up of two spores placed end to end. In each end there 

 appeared an eyespot, (fig. 6 c). 



One permanent slide shows a microzoospore 4.2 mic. in 

 width, 5 mic. in length, with two cilia. Another spore is 2.5 

 in width, 6.25 mic. in length and with two cilia. Another is 4.5 

 mic. in diameter and has two cilia. Still another, 4 mic. in di- 

 ameter, 7. 5 mic. in length, is biciliated. 



Since the material is remarkably pure, containing as far as 

 seen, only the Stigeoclonium, Pilinia and Palmella stages of the 

 main plant, together with a few Pediastrums and Diatoms dur- 

 ing the last of the period of cultivation, it seems proper to 

 connect these biciliated spores with the microzoospores devel- 

 oped in the plate cells. 



In addition to this there is a further demonstration of this 

 supposition. Pebbles "6" and "7" were kept in a tank by them 

 selves during the entire time. They were at first discovered to be 

 coated with very extensive layers of the plate cells which 

 looked very much like Coleochaete plates. Several times there- 

 after a microscopic examination was made, but nothing new 

 was noted. On the morning of April 27th, while changing the 

 water in the tank> an elongated streak of bright green color 

 was noticed on the side of the dish facing the light which fol- 

 lowed the surface of the water. It was caused by the presence 

 of young Pilinia thalli. No material in the Pilinia or Stigeoclo- 

 nium stage could be found in the tank. This seemed to prove 

 that the young Pilinia thalli resulted from the germination of 

 the microzoospores developed in the paJmelloid cells. 

 Cienkowsky's observations brought him to the conclusion that 

 the microgonidia of the Palmella cells developed into the origi- 

 nal filamentous alga, but he was unable to determine whether 

 the germination always followed the same course. Compare 

 also in this point Reinhart (I). 



