•Oct. 13,1923 
A New Tumor of the Apricot 
55 
A delicate whitish mycelium was noted four days afterwards forming 
on the inoculated cuts. In the course of two weeks acervuli, bearing 
spores typical of Monochaeti sp., formed on the lips of the three erup¬ 
tions. It was from this source, as well as from the acervuli which were 
found on the margins of the eruptions on one of the inoculated branches 
which was left untreated, that spores were obtained for the study of the 
morphology of the fungus. 
Spores of Monochaetia sp. were recognized in one or two instances 
among a variety of spores of different fungi obtained from the surface 
of the galls on Moorpark apricots. 
A microscopic search was made without success for organisms in the 
tissues of the gall. This negative result may be attributed in large 
measure to the extreme difficulty of obtaining sections thin enough and 
sufficiently well preserved for study, particularly from the region where 
cork and phloem are mixed. The phloem when free of cork is much 
more easily sectioned, and in this region a careful search was made for 
mycelium, without any positive result. In this connection the combined 
Del afield’s haematoxylin and alcohol-eosin stain, recommended by 
Durand (1) for the purpose of bringing out intercellular mycelium, was 
generally used. Further experimentation with a greater variety of 
stains, and perhaps the celloidin method of imbedding, would be neces¬ 
sary to bring this phase of the work to a successful completion. 
While the chain of evidence required by Koch’s rules for etiology and 
proof is incomplete, the writer believes that Monochaetia sp. is the causal 
agent of the Moorpark apricot gall. This belief is based on the suc¬ 
cessful inoculation and reisolation experiments discussed previously. 
THEORY CONCERNING THE MODE OF INFECTION 
No experimental data are at hand on the manner in which the parasite 7 
finds entrance into the tissues of the host. It may be worth while, 
none the less, to record some observations made on this subject. 
In no case have any eruptions been found in connection with wounds 
of mechanical or animal origin. The young galls are always associated 
with cracks in the bark of the tree. While these cracks may be the 
effect of the extrusion of gall tissue, and may not represent the road 
through which the parasite makes its way into the bast, a curious cor¬ 
relation has been noted between the extent of the cracking which takes 
place in the bark of the Moorpark apricot and the frequency of the disease 
in this variety. By comparison with the relatively resistant Blenheim 
variety the bark of the Moorpark shows not only a more extensive but 
also a deeper cracking. Although many Blenheim trees have been 
found which could not be distinguished from Moorparks on the basis of 
the appearance of the bark, the difference generally holds good and 
seems quite obvious when the comparison is made between groups of 
trees, as, for instance, between adjacent rows of the two varieties. No 
less suggestive is the fact that the disease attacks the trees during old 
age, a period in which cracking of the bark is characteristic, and never 
occurs on young trees. Thus, while the question of the mode of infection 
must be left in doubt until settled by empirical evidence, the theory 
that the parasite enters the tissues of the host through cracks which form 
7 The writer’s experience with this disease leaves him in no doubt that it is of parasitic origin. Support 
of this view is also given by results obtained from crude inoculations made by Earl Morris in 1917, at San 
Jose, Calif., who reproduced the galls by inserting bits of gall tissue into the bark of healthy apricot trees. 
