1906] CURRENT LITERATURE 313 
NOTES FOR STUDENTS. 
Mosaic disease of tobacco.—In an extensive account of the mosaic disease 
of tobacco, which he has been investigating for a number of years, HUNGER® 
deals somewhat radically with the theories that have been advanced to account 
for the disease, and gives, as he believes, a new explanation. The earlier bac- 
terial theories of Mayer, PritttEux, DELAcrorx, and others are treated only 
as matters of historical interest, since they are based on insufficient evidence. 
The more recent work of IWANOWSKI receives a more extended notice, although 
his view of the bacterial nature of the disease is likewise refuted, as HUNGER 
has been unable in his own investigations to corroborate IwANowSKI’s work. 
BEIJERINCK’s theory that the disease is caused by an active fluid substance, itself 
capable of growth, is discredited on the ground that BEIJERINCK was unable to 
show that the virus was able to increase in quantity outside of the plant, and 
that his proof of the fluid nature of the virus (diffusion in agar) is not sufficient. 
Against the enzyme theory of Woops the author raises two principal objections: 
(t) the transferability of the disease without limit does not accord with the 
properties of enzymes, whose activity is diminished by extreme dilution; (2) 
the virus of the mosaic disease has the property of being able to diffuse through 
parchment, a property not possessed by enzymes. 
HUNGER advances the view that the mosaic disease is due exclusively to dis- 
turbances of metabolism, the outward manifestation of which is the peculiar 
form of variegation seen in the leaves. That the mosaic disease, to whatever 
cause it may be attributed, is a result of disturbances of the metabolic processe: 
of the plant is beyond cavil; how this stat t brings us any nearer t pl a 
tion of the ultimate cause of the disease is beyond our comprehension. The 
author regards the disease as a sort of latent property possessed by tobacco 
plants, in which it may develop spontaneously if conditions are favorable, or to 
which it may be communicated by grafting and other methods. It is to be 
regarded as a kind of communicable variability! The active cause of the disease 
he regards as a toxin normally produced in the plant, but not injurious except 
under special conditions, when it accumulates in excess of the normal amount. 
The toxin is not like BEIJERINCK’s substance, capable of active growth, but is 
capable, when entering into a normal cell, of producing there catalytic effects, 
in consequence of which the toxin is there regenerated secondarily. In the 
words of the author, it is physiologically autocatalytic, all of which is perhaps 
merely a more extended theoretical explanation of what is ordinarily termed 
Srowth. HUNGER discusses also the etiology of the disease, and the probable 
telation of the methods of selection of tobacco practised at Deli to the rapid 
increase of the disease in the Sumatra tobacco districts. He points out that in 
order to obtain a high grade wrapper-leaf it has for generations been the practice 
of the tobacco growers to select for seed the plants with the thinnest leaves. This 
rn 
“ *Huncer, F. W. T., Untersuchungen und Betrachtungen iiber die Mosaik- 
rankheit der Tabakspflanze. Zeitschr. Pflanzenkr. 15:257-311. 1 
