644 Third European Journey 



yellows, mosaic and related diseases": three" very instructive 

 papers from different angles on Mosaic diseases by B. M. Duggar, 

 [H.] Klebahn, and Kunkel." He quoted Duggar as saying that 

 " poke weed juice in sufficient amount ' kills ' tobacco mosaic 

 virus." A full half-page memorandum from Dr. Kunkel's 

 " Studies of the aster yellows disease " read: 



Aster yellows cannot be given to Rosaceae but it is inoculable into plants 

 of many other families, can be budded like peach yellows, dwarfs the plant ' 

 and causes it to send out numerous chlorotic shoots of erect habit, and 

 often causes the flowers to become green. It is not transmitted by the juice, 

 but by a leaf hopper. . . . One day's feeding on a diseased plant is enough 

 to infect the hopper but he cannot transmit the disease to healthy plants 

 until the virus passes through an incubation period in his body the shortest 

 time for which is ten days.' 



166 



More than this, while examining an exhibit of " Opuntias inocu- 

 lated with an exceedingly destructive bacterial soft rot obtained in 

 Bermuda," Smith saw "various mosaic preparations including 

 those of Ray Nelson in squash petiole where were numerous 

 bodies stained with iron haematoxylin and looking like pro- 

 tozoans." He saw also G. P. Clinton's " amoeba-like bodies in 

 living trichomes of mosaic tobacco and . . . also in many other 

 cells. Clinton," he said, " can get mosaic, he claims, from dried 

 mosaic tobacco twenty years old (done by finger rubbing) ," and he 

 noticed that the Connecticut plant pathologist's " stain 1% iodine 

 green in l%acetic acid differentiates the amoeboid bodies from the 

 nucleus." He examined also Miss Eckerson's " stained smear pre- 

 parations of tomato mosaic," and Miss Goldstein's " striking slides 

 of tobacco mosaic stained with 1% iodine green in 1% acetic acid. 

 The amoeboid bodies pink in contrast to the blue nucleus." ^''^ 



These exhibits were seen on the day before he gave his address, 

 " Fifty Years of Pathology." Into this he had written several 

 paragraphs on the current study of plant viruses and protozoa. 

 He knew something of Duggar's work. At the spring meeting of 

 the National Academy of Sciences, Smith had introduced him when 

 he read a paper on " Indications respecting the colloidal behavior 

 of the agency of virus inducing mosaic disease of tobacco." "^ By 



"' Diary, Aug. 18, 1926. 



"' Diary, Aug. 19, 1926. 



^°* Diary, Apr. 27, 1926; and program of the meeting. At ttiis meeting Smith also 

 presented his paper, Changes of structure due to a modified environment: a study of 

 labile protoplasm in Helianthus annuus L. 



