104 
leaves. In this there is an analogy with 
the condition called “clustering” or 
“brachysm,”’ which is a feature of some 
varieties of Upland cotton in the United 
States. In some varieties brachysm is 
definitely hereditary, while in others the 
shortening of the joints has relation 
to external conditions. But in bra- 
chysm only the joints of the fruiting 
branches are shortened, whereas the 
club-leaf disorder also affects the inter- 
nodes of the main stalk and the vegeta- 
tive branches. The shortening, like the 
abnormal branching, is carried farthest 
in the Chinese cotton, not so far in the 
Upland, and is still less apparent in the 
Sea Island and Egyptian types. 
REDUCTION AND DISTORTION OF 
LEAVES 
In severe cases of club-leaf the leaves 
are greatly reduced, often to less than 
half the normal size, and are twisted 
and crumpled over the entire surface, 
with a general arching or bending back 
of the midrib and principal veins, so 
that the lobes and margins of the leaf 
are turned under. In the native Chin- 
ese cotton these symptoms are carried 
somewhat further than in the foreign 
varieties, though Upland cotton also is 
severely affected, and sometimes the 
margins and lobes are rolled under 
more abruptly and regularly than with 
the Chinese cotton. (Compare Figs. 
1 and 2 with Figs. 5 and 9.) 
DISCOLORATION OF LEAVES 
Though the discoloration differs in 
extent with varieties and conditions, an 
angular mottling of the web of the 
leaves is a regular feature of the club- 
leaf disorder, beginning along the 
margins and advancing into the thinner 
tissue between the lobes, though keep- 
ing away from the principal veins. At 
first the discoloration is only a paler 
and more yellowish-green, which con- 
tinues in the Chinese cotton to the end 
of the season, but in Upland cotton a 
reddish tinge soon becomes appreciable 
and gradually becomes more _ pro- 
nounced. Late in the season, a deep 
The Journal of Heredity 
red color renders the fields of Upland 
cotton strikingly different from the 
native Chinese cotton, even at a dis- 
tance. 
Among the Upland varieties grown at 
Nanking University and at the Wu- 
chang Experiment Station, the Durango 
reacted most strongly in regard to dis- 
coloration and distortion of the leaves, 
and Columbia the least, but the Colum- 
bia seemed to be less mature than the 
other varieties, and maturity may be a 
factor in bringing the disorder into ex- 
pression. 
Connected, perhaps, with the more 
pronounced color reaction, is the fact 
that when affected plants of Upland 
cotton suffer from drought or other 
unfavorable conditions, the discolored 
portions of the leaves may dry out and 
die, the death of the tissue taking the 
same course as the discoloration, begin- 
ning at the margins, following back be- 
tween the principal veins, and leaving 
a band of tissue alive along the veins. 
The discoloration of the leaves, in 
connection with the other symptoms, 
suggests that the club-leaf may prove 
to be one of the so-called mosaic dis- 
eases, the causes of which are still 
obscure, though some of them, such as 
the sugar-beet disease of the United 
States and the sugar-cane disease of 
Hawaii, are supposed to be transmitted 
through the agency of insects. On the 
other hand, analogy with the leaf-curl 
caused by the plant-lice might account 
for club-leaf without supposing that a 
germ or parasitic organism is involved. 
Though the injuries are more serious 
than those of leaf-curl, there is a similar 
limitation to the growing tissues, with 
no appreciable effect upon the parts that 
have developed earlier in the season. 
The injury as a whole may be con- 
sidered as a generalized gall-formation 
modifying the growth of the plant while 
the insects are active, but not affecting 
the tissues that are formed before or 
after. The discoloration symptom is 
lacking in the plant-louse disorder, but 
some galls are highly colored and others 
not. The club-leaf is not transmitted 
