143 
Dale . — A Bacterial Disease of Potato Leaves . 
surrounded by a thick wall. The contents of the ripe spores show marked 
apical staining (Fig. 1 6, e). Most frequently two spores are formed in 
a short rod, or segment of a rod. In some cases a long rod breaks up 
into many spores, some of which do not attain to maturity. In the case of 
a short rod with two spores, only one may develop fully (g). 
A portion of zoogloea with the vegetative rods embedded in a gelatinous 
matrix is seen in Fig. 1 6,h. 
4. Infection Experiments. 
Attempts were next made to infect potato leaves, both of seedlings and 
of mature plants, with the organisms described above. Some of these 
experiments were made in 1910 and the others in 1911, some in a green- 
house, others in the open. In both years the climatic conditions were 
unfavourable for experiments in the field. In 1910 the weather was so 
damp that the plants soon succumbed to Phytophthora. In 1911, on the 
other hand, the heat and drought were so great that, except early in the 
year, the Bacteria all dried up before they were able to enter the tissues of 
the host. 
1. In 1910, owing to an unavoidable interruption in the work, the in- 
fections could not be made until August. Cultures of Bacteria from both 
leaf and tuber were used. The latter gave negative results, however, and 
they were consequently abandoned. 
Bacteria from the same culture tube were used to infect both the seed- 
lings and the mature plants. In some cases the Bacteria were laid on the 
leaf and left to find their own way in ; in other cases a wound was made 
with a platinum needle which had been first dipped into the culture. 
The infections were made on August 13. The seedlings used had 
been grown in a greenhouse and were infected in situ . By August 29, 
i. e. in sixteen days, the infected leaves showed symptoms of leaf-curl, and 
were also turning brown in places. Some of these leaves were fixed in 
chrom-acetic acid and examined later. 
The mature plants, grown from tubers, were some of an unusually late 
crop which appeared to be healthy, although most of the potatoes in the 
neighbourhood had been badly attacked by Phytophthora . The infections 
were also made on August 13. As in the case of the seedlings the organism 
obtained from tubers did not infect the leaf. The Bacteria were either laid 
on the leaves, which were wet with rain, or were stabbed into the tissues with 
a platinum needle. At first the infected plants were covered with bell- 
glasses and shaded with cloths. The glasses were removed after three days, 
but the cloths were retained as a screen from the sun and also as a possible 
protection from the attacks of Phytophthora. By August 29 several infected 
shoots showed signs of leaf-curl and of browning. These were fixed in 
methylated spirit. 
