THE METHOD OF MOVEMENT 213 



little or no carbohydrate, and move into them only slowly 

 or not at all even though they may be receiving carbo- 

 hydrate, and that they move rapidly to growing tissues 

 independently of the position of the growing tissue, might 

 be interpreted as indicating that the growth condition 

 of the tissue is more important than the direction of 

 movement of carbohydrate. Schumacher (1933) found 

 that outward transport of fluorescein was in like manner 

 unrelated to carbohydrate transport. The fact that viruses 

 are negatively charged may be a factor in determining their 

 distribution. It is possible that the direction of movement 

 of both virus and certain solutes is determined by the 

 movement of protoplasm of a certain type, whereas other 

 material, perhaps bearing a different electrical charge or 

 held in different layers of protoplasm, may be moving in 

 the opposite direction. Although movement may be 

 partly determined by electrical charge, the effect may be 

 different from that on growth substance for the movement 

 of the latter seems to be strictly polar. Smith (1931) 

 reports the interesting fact that in experiments on the 

 behavior of a mixed virus in tobacco, although the x strain 

 develops more rapidly at the point of inoculation, the y strain 

 seems to travel to distant parts much more rapidly. 

 Bennett (1932) reports a comparable case in which, of 

 two types of raspberry mosaic both of which are probably 

 transported through the phloem, one moves much faster 

 than the other. Whether these observations mean that 

 the different strains of virus move in different cells, in 

 different parts of the same cell (perhaps in different layers 

 of mo\dng protoplasm), or one is delayed more at obstruc- 

 tions of course is not known, but they seem to oppose 

 the concept of a unidirectional mass flow of all phloem 

 contents. 



The various transportation studies with viruses may 

 prove to be of great value in helping to solve general 

 translocation problems. But until they are supported by 

 other evidence I rather hesitate at present to accept them 

 as indicating normal movements, for some of them bring 



