MISSOURI BOTANICAL GARDEN BULLETIN 159 
ease within a week or two. From the point of infection the 
disorder spreads rapidly to various parts, since the juice of 
the diseased tissue is extremely virulent. One part of this 
substance in 10,000 parts of water has been shown to be 
capable of producing a serious attack of the disease, and 
dried plants are known to retain their ability for reproduc- 
ing the disease in other plants for at least two years. It will 
readily be seen how easy it is to communicate such an infec- 
tion from plant to plant, and the loss due to ‘‘chlorosis” dis- 
eases of such crops as tobacco, tomatoes, peaches, beets, etc., 
is very serious. 
Perhaps the so-called “mosaic disease” of the tobacco, due 
to an infectious chlorosis, has been most carefully studied. 
This disorder may appear in the seed beds while the plants 
are still small, but more often it occurs in the mature plant 
in the field. The mosaic usually develops first in the very 
young leaves and when once started is practically incurable. 
The first apparent symptom is a mottling of the leaf, due to 
the partial disappearance of the chlorophyll, in irregular 
blotches. At these points the tissue does not develop nor- 
mally, and the unequal growth causes a crinkling of the leaf 
as shown in the accompanying plate (Plate 11). Still later 
there may be produced long narrow leaves which ultimately 
may develop into nothing more than thin string-like 
strands, this latter condition occurring most frequently in the 
tomato (Plate 11). All plants thus affected are, of course, 
stunted because of the malnutrition induced by the absence 
of chlorophyll. 
Various theories have been advanced as to the cause of 
the mosaic disease of tobacco and tomato. While some have 
held that the elimination of the chlorophyll is due to a micro- 
organism so small that it cannot be detected with the micro- 
scope, others believe that the disease is due to a local dis- 
turbance of the ferments of the cell or the production of 
toxins, and that these substances transferred from an affected 
plant, are capable of creating the diseased condition in the 
young tissues of the other plants. 
HOLLY AND MISTLETOE 
Holly and mistletoe are inseparably associated with the 
Christmas season, not only on account of their beauty and 
persistence during the winter months, but because from 
earliest times these two plants have, by tradition, been linked 
with the life of Christ. The most plausible origin for the 
