THE GARDENERS' CHRONICLE OF AMERICA. 
23 
which show what is supposed to be non-infectious variega- 
tion are Bougainvillaea glabra Samderiana, Fittonia 
argyroncura, the silver-banded geranium (Pelargonium 
hortorum var. albo-marginatum) , varieties of elephant's 
ears (Caladium), which show some of the most remark- 
able instances of absence of chlorophyll, as well as the 
numerous striped and banded grasses. 
An interesting example of what is apparently an infec- 
tious chlorosis may be seen in the whitened tips of the 
club moss (Sclaginella Kraussiana). Such variegated 
forms are always propagated by cuttings, but are never 
inherited through the seeds. This is not true, however, 
of the variegation due to non-infectious chlorosis, which 
is perpetuated through the seed. If the juice of a plant, 
like tobacco, having an infectious chlorosis comes in con- 
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 normally, and the unequal 
growth causes a crinkling of the leaf as shown in the ac- 
companying plate. 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. 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 
I. MOSAIC DISEASE HI' TOBACCO. -'. FITTONIA ARGYRONEURA SHOWING WHITE VEINATION. 3. PELAR- 
GONIUM HORTORUM VAR. U.BO-MARGINATUM, SHOWING CHLOROSIS. 4. MOSAIC DISEASE OF TOMATO. 
tact with a wound on any part of a normal plant of the 
same kind, the latter may show symptoms of the disease 
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 
reproducing the disease in other plants for at least two 
years. It will readily be seen how easy it is to com- 
municate such an infection from plant to plant, and the 
loss due to "chlorosis" diseases 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 
to a micro-organism so small that it cannot be detected 
with the miscroscope, others believe that the disease is 
due to a local disturbance of the ferments of the cell or 
the production of toxins, and that these substances trans- 
ferred from an affected plant, are capable of creating the 
diseased condition in the young tissues of the other plants. 
(Editor's Note: We are indebted to tin' Missouri Botanical 
Garden Bulletin for this contribution and accompanying illus- 
trations. ) 
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