July i, 1925 Overwintering and Dissemination of Cucurbit Mosaic 
27 
SYMPTOMS OF MOSAIC ON MILKWEED 
The symptoms of the mosaic disease on the milkweed are similar 
in character to those found on the cucurbits. Mosaic plants are 
easily recognized by their dwarfed growth and mottled and distorted 
leaves (pi. 2, A, B). Mosaic milkweeds rarely reach a height of more 
than 2 feet, while normal plants usually attain 3 to 4 feet. Mosaic 
leaves are ordinarily mottled with irregular patches of greenish yel¬ 
low". These areas are larger proportionately than in the case of the 
cucumber, and the mottled appearance is ordinarily more marked 
in character. This mottled character varies, however, with the 
individual plants and is occasionally much less pronounced (pi. 2, 
D, E, F). 
The leaves of mosaic milkweeds are distorted in shape to an extent 
which is uncommon in the cucurbits, and the symptoms in this regard 
are more suggestive of the mosaic disease on tobacco. The leaves 
are ordinarily smaller than those of the normal milkweed and usually 
are more lanceolate than the oblong to ovate leaves of healthy plants. 
In some instances the leaves are of abnormal length and taper rapidly 
from a broad base to an almost filiform tip. Very commonly half 
of the leaf blade develops to almost normal size while the other half 
is only a few millimeters wide for all or part of its length. This effect 
of the disease produces abnormalities which are readily recognized. 
The leaves of mosaic plants also show a tendency to curl upward at 
the margins, producing a cuplike effect in extreme cases (pi. 2, B). 
The dwarfed character of the plants, many of which are not more 
than 12 inches high, accompanied by the characteristic symptoms 
on the leaves, make the mosaic disease easily recognizable in the field. 
It has been found, however, that normal milkweed plants frequently 
show" a mottling of the leaves which may be confused with the true 
mosaic. Such plants are of normal height, however, and show none 
of the curling or distortion characteristic of mosaic. The mottling 
in such cases is also different from that produced by mosaic in 
that it usually consists of areas which are limited by the parallel 
lateral veins and extends from the midrib to the edge of the leaf. 
These areas produce a striped effect, while in the case of mosaic, the 
yellowish areas are less regular in outline and are scattered irregularly 
over the leaf. Symptoms similar to those described above have also 
been observed on a single plant of Asclepias amplexicaulis Sm., but 
no infection was secured from inoculations made from this plant to 
the cucumber. 
OVERWINTERING OF THE MOSAIC DISEASE IN THE MILKWEED 
Experiments with the Roots of Mosaic Milkweed 
Since mosaic shoots are produced each year from the roots of 
other mosaic perennials such as the pokeweed (Phytolacca decandra) (2), 
it was expected that the mosaic disease would be carried from year 
to year in the roots of the milkweed. Observations in the Olin plat 
at Madison, Wis., during 1919 and 1920 showed that mosaic milk¬ 
weeds appeared in the summer of 1920 at approximately the same 
points in which they had been noted during the preceding year. 
Experimental proof of such overwintering w r as obtained during the 
winter of 1920-21 in the case of roots of milkweeds brought in from 
the field and grown in the greenhouse. A number of mosaic and 
