1 38 Dale . — A Bacterial Disease of Potato Leaves . 
much resemblance, but the tubes in the potato leaf are the bigger, and 
in many cases the less branched of the two. The mode of entry in each 
case is similar, as the infection tubes of leguminous plants penetrate the cell- 
wall of the root-hair, while those of the potato plant pierce the thin cuticle 
of the leaf. In both cases there is frequently a swelling at the point of entry 
and a dilatation where the tube pierces the cell-walls of the host. This may 
be seen by comparing the diagrams of the different tubes (cf. figures in this 
paper with those in Miss Dawson’s). 
In both cases the tubes finally pass into cells which are filled with 
granules that stain like the tubes. It seemed probable, therefore, that in 
each case a similar organism was concerned. Attempts were accordingly 
made to isolate an organism from leaves in which tubes and granules had 
been found by previous microscopical investigation. These attempts were 
not made until 1910, as in 1909 the nature of the tubes was still undeter- 
mined. 
Leaves showing marked ‘ curl ’ were obtained from plants grown in 
a greenhouse from small but apparently healthy tubers which were planted 
on February 3. By March 11 — i. e., as in the preceding year, after about 
a month — tubes and stainable granules were found in the leaves. From 
pieces of these leaves Bacteria were obtained by means of plate cultures of 
gelatine containing extract of potato tubers. The leaves were remarkably 
free from Fungi or Bacteria, other than the one obtained, so that pure cultures 
were easily and quickly made. 
It may here be noted that various kinds of Bacteria were obtained from 
potato tubers , and compared with those from potato leaves , but in no case 
were they the same in their behaviour on culture media. 
In the spring of 19 ij, from a badly diseased plant, in which tubes and 
Bacteria were abundant, three kinds of organisms were obtained. One of 
these was identical with that isolated in 1910. Of the other two, one was 
an organism with a most remarkable habit of growth : on potato tubers it 
formed large Tremella-Mke. gelatinous masses, a centimetre or more above 
the surface of the tuber. 1 These masses were corrugated at the edges, and 
resembled a gelatinous fungus far more than Bacteria. The culture was not 
slimy but exceedingly tenacious, so that strong pressure with a cover-slip 
did not break it up. Microscopic examination showed that the gelatinous 
mass consisted of roundish, highly refractive Bacteria, embedded in masses of 
gelatinous substance, and relatively widely separated from one another. 
The third form was somewhat like the second, but so feebly growing 
that the culture of it was soon abandoned. 
The original Bacteria obtained from leaves in 1910 grew well on 
a number of media, but most successfully on pieces of sterilized potato 
1 This growth was confined to the cut surfaces of the tuber and never spread to the 1 skin ’ 
of the potato. 
