PLANT DISEASES AND FUNGI.
25
disease is really due to the microbe mentioned the malady differs
widely from that of any heretofore described bacterial injury to
living vegetation. The microbe must be sparsely but widely dis-
tributed through the still living tissues of the tree, in which it must
very slowly develop without causing evident local disturbance. This
latter especially is entirely at variance with known effects of parasitic
organisms. But we know that the peach tree affected with this
disease very gradually succumbs, lingering along several years with-
out local injury of pronounced type."6
On the subject of the California vine disease, Mr. Pierce, a
special agent sent to investigate the disease, states that yellow spots
occur on the leaves, which showed no trace of insects or fungi.
That "the peculiar appearance and location of these spots led to a
careful study of the same, which resulted in finding bacteria-like
bodies in large numbers, within the chlorophyllose cells of the spongy
parenchyma immediately surrounding the spiral vessels supplying that
region. After a long series of observations, made on material from
various portions of the diseased district, which in no case failed to
disclose the diseased vines as swarming with these bodies in all
portions where sap had a ready flow, he believed it proper to under-
take a series of experiments to determine if these bodies, always
present, bore any relation to the disease as a whole. He had little
doubt that they were micro-organisms, and gave to the local spotting
of the leaves their characteristically sharp outline. Cultures from
various parts of the vine were made in agar-agar, and other media.
Three sorts of bacteria were found with enough constancy to warrant
further study, but he had not, so far, been able to determine whether
any of these were the cause of the disease. In view of the fact that
several Italian students have for years claimed that an Italian disease
of similar characteristics is caused by bacteria, it is proper the
matter should be decided, if possible."7
It is established, then, beyond doubt, that bacteria inhabit the
tissues of plants in great numbers, that they appear to be of kinds
peculiar to those plants, and may, or may not, be the cause of some
of the plant diseases. To carry on the subject still further, we must
refer to a series of investigations on a disease of melons, and, by
the results of these investigations, exhibit a very strong presumption
that microbes are the cause of some diseases of plants.
6 "Report of the Secretary of Agriculture," U.S. Section of Vegetable Pathology for 1889,
p. 423.
7 Report for 1889, p. 427.