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ALLARD: MOSAIC DISEASE OF TOBACCO 443 
result of deféctive nutrition of the young dividing and rapidly 
growing cells, due to a lack of elaborated nitrogenous reserve food 
accompanied by an abnormal increase in activity of oxidizing 
enzyms in the diseased cells. The unusual activity of the enzym 
prevents the proper elaboration of reserve food, so that a plant 
once diseased seldom recovers. On the decay of the roots, leaves, 
and stems of both healthy and diseased plants, the enzym in 
question is liberated and remains active in the soil. The enzym 
is very soluble in water and appears to pass readily through plant 
membranes. If young plants take it up in sufficient quantity to 
reach the terminal bud, they become diseased in the characteristic 
Way.” 
In 1900 Heintzel (22), independently of Woods, came to the 
conclusion that oxidizing enzyms are responsible for the origin of 
the disease in tobacco plants. 
Loew (24) in 1900 published briefly on the mosaic disease of 
tobacco. The observations of a number of practical growers in 
Connecticut were mentioned, but opinions were shown to be 
widely different as to the origin of the disease. Loew showed 
that an encire field may become diseased in one year, followed 
by a healthy crop the next season. He noted the sporadic occur- 
rence of the disease. The oxidase and peroxidase content of 
healthy and mosaic plants was also compared. Many popular 
notions were cited which are too much at variance, however, to be 
regarded as established facts. 
n 1900 Koning (23) gave a rather full discussion of his work 
with mosaic. Although careful examinations were made for 
microérganisms in the diseased tissues, all results were incon- 
clusive. 
Koning inoculated many healthy plants with soil solutions 
from fields where mosaic was prevalent. He was never able to 
produce mosaic in this way, and concluded that the virus could 
not exist long in the soil in an active condition. He stated that 
filtering the sap once through a Chamberland filter did not render 
it inert, but that when twice filtered its infectious nature was lost. 
He finally concluded that the virus of mosaic contained micro- 
Organisms too small to be retained by the pores of the filter, and 
that these possessed vegetative and spore-forms. Other conclu- 
