442 



BULLETIN 387 



of the spores as from 1.8 to 2.211, and Pinoy (1907), altho he does not 

 state directly, says in speaking of swarm-spores that they are from 3 to 4 n 

 in diameter. 



The measurements made in connection with the present experiments 

 agree more nearly with those of Pinoy for the swarm-spores. The spores 

 in formation, when not yet spherical, measure from 2.5 to 6.9 p. in diameter, 

 being much more variable than those that are older. The smallest mature 

 spore measured was 1.9 j*, and the largest was 4.3 JJL. These measurements 

 include not only living spores but also those stained in various ways. 

 The average was 3.3 //. 



A SIMILAR ORGANISM 



For some time the writer was at a loss for an explanation of the occasional 

 presence of from two to twelve strange nuclei in certain root hairs and 

 epidermal cells (fig. 109, A). These are from 3 to 4 n in diameter, 



B 



FlG. 109. AN UNKNOWN ORGANISM ASSOCIATED WITH PLASMODIOPHORA BRASSICAE 



A, Nuclear-like bodies in a root hair, probably swarm-spores of Olpidium Brassicae; B and C, an 

 unknown organism in the epidermal cells of a cabbage root, probably Olpidium Brassicae. X 800 



being smaller than the nuclei of the host cells. The nucleoli have a 

 much denser content than those of the host cells, and are much smaller 

 and less prominent. They appear to be entire swarm-spores containing 

 no visible cytoplasm; however, they do not resemble those of Plasmodi- 

 ophora Brassicae, being larger, and, most important of all, not having the 

 hyaline zone about the nucleolus which is so characteristic of the latter. 



