[Vol. 10 



198 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



Michigan A gricultural Experiment Station (Nelson, '22) . Besides 

 the bean mosaic, similar diseases of clover and tomato, and the 



leaf roll of potato are reported 



may 



not have appeared remarkable at the time the paper was presented 

 but it is significant now that Nelson gave no picture of the condi- 

 tions in the comparable cells of healthy plants. In two places in 

 the printed paper (Nelson, '22) he refers to healthy tissue, one 

 reference being to the potato, where he says, in part, "No 

 organisms have been found in the sieve tubes of these plants in 

 all the slides examined;" whereas in a general discussion of re- 

 lationship he affirms that "the finding of definite protozoan 

 organisms in constant association with mosaic plants and their 

 absence from healthy ones indicate that they are probably the 

 factor so long sought as the cause of these diseases." 



We have endeavored to supplement this work with an elaborate 

 cytological study of healthy and diseased tobacco and tomato 

 tissue, healthy bean tissue, and healthy cucurbit tissue. In the 

 Solanaceous plants we find in the phloem and in other elongated 

 cells of perfectly healthy individuals precisely the same bodies 

 that are found in diseased tobacco and tomato plants. The 



number of 



The most 



characteristic of these bodies are often sinuous, or screw-like, 

 also of other types. They are usually homogeneous and often 



1) 



Some supernumerary nuclei or 



cytoplasmic aggregates are also observed, and the remains of 

 plastids may be associated with these. We have 1 not studied 

 diseased bean tissue, but in healthy tissue the long cylindrical, 

 ovoidal, or elliptical bodies are generally homogeneous in char- 

 acter, centrally disposed, and frequently associated with cyto- 

 plasmic strands, the latter giving the appearance of one or more 

 flagellae at the ends. It seems apparent that these particular 

 bodies are those that have been described by Strasburger in 

 normal sieve tissue 1 . In certain cucurbits, notably in Chayote 

 edule, disintegrating plastids in cells undergoing rapid elongation 

 present the appearance of organisms of various types, all more 

 or less nodose. It seems unnecessary to describe 



further 



the 



by Nelson are all to be found, but 



