212 TRANSLOCATION IN PLANTS 



in the apical growing parts but this was not clearly proved 

 to be due to more rapid transport. There seemed to be an 

 approximate relation between the completeness of spread 

 of the virus and the relative amount of food supplied by 

 the inoculated leaf to the rest of the plant. That is, if the 

 inoculated leaf was shaded and other leaves not shaded, 

 the subsequent distribution of virus throughout the plant 

 was markedly unsymmetrical, perhaps indicating a small 

 amount of inoculum, whereas if the inoculated leaf was 

 not shaded the unsymmetrical distribution was greatly 

 reduced, and when two other leaves were shaded so that 

 the inoculated leaf was supplying a large part of the 

 carbohydrate for the plant, the unsymmetrical distribution 

 was completely lacking. In these experiments of Holmes 

 there was no way of determining the actual velocity of 

 movement for the time necessary for incubation and 

 entrance of the virus into the phloem was included in the 

 total time necessary for movement. 



Samuel (1934), working on the movement of tobacco 

 mosaic in tomato plants, found the virus to move from the 

 point of inoculation on a leaflet near the middle of a plant 

 to the root at a distance of about 60 cm. within 12 hr. 

 after the entrance into the phloem. But, contrary to the 

 type of behavior observed by Bennett, the virus during 

 the next 12 hr. or less moved rapidly from the roots to the 

 younger tissues at the top of the plant, a distance of 

 approximately 90 cm. This would indicate a movement 

 between 1 and 2 mm. per minute. This movement from 

 the root would seem to be in the reverse direction of that 

 of the major movement of food. The direction of move- 

 ment seemed to bear no relation to the time of day and 

 would seem for this reason also to be unrelated to food 

 movement. Movement during the first 12 hours seemed 

 to be in the direction of food movement, for the virus 

 usually moved into developing fruits independently of 

 whether they were below the point of inoculation or one 

 or two internodes above. 



The fact that viruses seem to move out of older leaves 

 even when they have been darkened and are exporting 



