144 
July, 1889. 
ORCHRRDte’l GARDEN 
CONDUCTED BY PROF. F. LaMSON SCRIBNER, 
Botanist. Experiment Station, Knoxville, Tenn. 
Peach-leaf Curl. 
(Taphrina deformans.) 
The peculiar disease of the leaves of the 
peach known as “curl,” is familiar to all 
growers of this fruit. It is wide-spread 
both in this country and Europe, probably 
occurring wherever the peach is cultivated, 
and although not generally regarded as a 
serious malady the damage resulting from 
it is by no means insignificant. It often 
severely injures nursery stock, and young, 
thriftily growing trees are more subject to 
its attacks than those which have reached 
a degree of maturity. Young trees, obtain- 
ed from New York nurseries and planted 
here last year on the University grounds, 
have been very badly affected with the 
Fig. 1595. 
“curl" this season. Nearly 50 per cent, of 
the first leaves formed were destroyed and 
the attack was not limited to the foliage; 
the disease extended to very many of the 
young and rapidly growing shoots, and all 
such were killed before the first of June. 
The older peach trees in this neighborhood, 
grown here from pits, have shown the dis- 
ease but rarely, only here and there a single 
diseased leaf. 
The “curl” is limited in duration to the 
the period when the young shoots and 
leaves are most tender; after the tissues of 
these parts are fully formed or matured 
they are no longer affected. The disease 
becomes manifest as soon as the first leaves 
are expanded and, in this latitude, its 
course is run before the end cf May. By 
the first of June the only signs of the mala- 
dy are the withered leaves scattered on the 
ground and the dead and shriveled shoots 
on the tree; new leaves have already 
been developed on laterals which have 
grown from the branches below that por- 
tion killed by the disease. On some of the 
dead twigs there is a gummy exudation, 
probably the product of unassimilated sap. 
The illustration (Fig. 1600) shows the 
characteristic appearance of a peach leaf 
affected with the “curl,” and the same fig- 
ure illustrates a twig diseased from the 
same cause. Such leaves are too familiar 
to the readers of Orchard and Garden to 
require a detailed description, we would 
only add that not infrequently the entire 
leaf is involved, especially those not more 
than half grown, and when this occurs the 
leaf is usually curled or twisted upon itself. 
We have often seen a half dozen or more 
such leaves clustered at the ends of the 
young shoots. The diseased leaves or parts 
of leaves affected are somewhat thicker 
and of a more fleshy texture than those in 
health. The under surface of the diseased 
parts is usually smooth but the upper sur- 
face has a more or less mealy appearance. 
The Peach Leaf Curl. Fig. 1600. 
Sometimes, though rarely, this mealiness 
is seen on the under surface of the leaf, but 
we have never seen it on the diseased leaf 
stalks or shoots. The surface of the latter 
is always smooth. When the leaf-stalks 
are affected they are swollen to several 
times their normal thickness and seldom 
attain their full length. On the shoots the 
disease may be limited to a portion of the 
circumference or, as is more often the case, 
involve the entire surface. These shoots 
have a pale green color, are much thicken- 
ed, the surface being irregularly swollen 
and in the end they die and turn black. 
The cause of peach-leaf curl is a minute 
fungus which the mycologists have named 
Taphrina deformans. This fungus is closely 
related to, in fact possesses all the essential 
characters of Taphrina pruni, which causes 
the inflated and bladdery “plum pockets,” 
which will be described in the August num- 
ber. In the tissues of the diseased parts, most 
readily in the leaves, one may see the my- 
celium of this fungus — the Taphrina defor- 
mans — extending its growth between the 
cells and sometimes even passing through 
them. In the deeper tissues the threads 
are scattered and of very irregular growth 
(see upper fragment in fig. 1595). Just be- 
neath the cells of the epidermis of the leaf 
the mycelium is more abundant, but in no 
part is it so profuse as between the epider- 
mus and the cuticle. Here it forms a per- 
fect net work of threads, which owing to 
the shape of the individual cells composmg 
them, resemble strings of irregularly form- 
ed beads. A bit of this peculiar mycelial 
growth taken from between the cuticle and 
epidermis of the upper leaf surface, is 
shown in figure 1595. It is from the cells 
of this mycelium that the fruiting or spore- 
bearing sacks of the fungus are developed. 
Fig. 1594. 
These are produced in great numbers, grow- 
ing up through the cuticle and imparting 
to the surface the mealy appearance already 
referred to. An exceedingly thin section 
made vertical to the leaf surface, is shown 
in figure 1594. Fragments of mycelium are 
seen in the tissues as at d. Between the 
cuticle and the epidermis are a few of the 
beadlike cells c of the network described 
above. A young spore-sack is shown at b, 
while at a is a mature sa;k containing 
spores. These spores doubtless serve to 
spread the disease from leaf to leaf and 
from tree to tree, but all efforts made to 
produce infection artificially have so far 
failed of results. Nothing is really known 
of what becomes of the spores or of the 
fungus after it has run its course and the 
effects of its ravages have disappeared. It 
is probable, however, that portions of the 
mycelium remain dormant in the tissues of 
the tree near the buds from one season to 
the next, awaiting the tender, spring growth 
to produce anew the disease. It is evident 
that it is only possible for the fungus to at- 
tain any marked development except at the 
commencement of the growing season 
w^hen the tissues of the young trees are suc- 
culent and most tender. When these tis- 
sues reach a certain degree of firmness the 
fungus has no longer the power to penetrate 
between the mature cells. It is not neces- 
sarily wholly destroyed, but, as just stated, 
