208 MISCELLANEOUS EXAMPLES 



In Fig. 30 ( X 375) some of the combinations that have been met 

 with are shown. In A four small spaces are represented. In ^he 

 upper one Algoid segments and Diatoms are intermixed ; in the 

 one on the left young Diatoms were seen forming — the contents 

 of this space being distinctly paler than those of the other two 

 spaces in which the Diatoms were more fully formed and more 

 closely packed together. In B, two or three fused contiguous 

 spaces are shown in which Algoid cells and Diatoms, together 

 with various intermediate forms, were intimately intermixed ; while 

 C is the only space that I have yet found in L. trisulca containing 

 Diatoms as large as are there represented. They were mixed with 

 Chlorochytrium cells, as well as other minute Diatoms, though the 

 latter are not recognisable in the photograph. 



Another point is also of much importance, and that is, the 

 frequency with which Diatoms may be seen around the periphery of 

 spaces still densely crowded with Chlorochytrium products which have 

 not yet begun to emerge. These Diatoms, therefore, make their 

 appearance within closed cavities, and often in regions far removed 

 from the original point of entry of the active Algoid spore. No 

 infection hypothesis, even backed by a further hypothesis of 

 chemotaxis, is, I submit, capable of explaining the presence of 

 these Diatoms. They are evidently formed where they are found 

 by a transformation of the Algoid cells, and different stages of the 

 process may often be clearly recognised — the spherical cells, as 

 I have said, becoming elongated, and changing from a bright 

 green to a brownish-yellow colour as they take on the forms of 

 the Diatoms.' 



(b) On the Origin of Anabena from the Cells of Chlorochy- 

 trium lemnae. 



In the memoir by Ferdinand Cohn, " Ueber Parasitische 

 Algen,"'' in which this Chlorochytrium was first described as 

 infesting Lemna trisulca^ he figures four diiferent kinds of organ- 

 isms as occasionally to be met with in spaces that had been 

 previously tenanted by Chlorochytrium, namely, a species of 

 Raphidium, of Mastigothrix, of Leptothrix and of Nostoc. He 

 assumed that these were all parasites which had, in some way, 



' See also " Studies in Heteiogenesis," p. 183, concerning the origin of Diatoms 

 from Algoid cells of another kind which are often found infesting the different 

 species of Duckweed. 



2 " Beitriige zur Biologie der Pflanzen," 1872, p. 97 



