ha reesl 
INFECTION THROUGH WATER-PORES. 57 
campestre diffused in sterile water (plate 2, and figs. 9, 10). The infection of the black rot 
takes place through water-pores of the cabbage, turnip, mustard and various other plants 
of the family Cruciferae, and the bacteria may be traced very readily from the substomatic 
chamber down into the vascular system of the leaf until they disappear, and have been so 
traced by the writer in a number of instances in serial sections made from properly fixed 
and suitably infiltrated material (see vol. 1, figs. 76 to 79 and 115 to 117). The infection of 
cabbage plants through the water-pores was confirmed by Russell and Harding in 1898, 
and was also obtained in kohlrabi by Hecke in 1902, and more recently in cabbage by 
Brenner, one of Dr. Fischer’s special students. As the writer stated in January 1898 
(Farmers’ Bulletin), the separate water-pore infections on a single large plant occasionally 
number several hundred, while very frequently the disease with its conspicuous black 
venation may be seen extending into the leaves of the plant from fifty or more leaf-serratures. 
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Fig. 11.* 
If the bacterial black rot is at all prevalent in a field, infections of this sort are as common 
and as easily observed as the plants themselves, and the bacteria may be demonstrated 
in abundance in sections made through any of the distinctly blackened leaf-serratures, and 
in a certain proportion of them before any stain is visible. For a time the bacteria are 
restricted to the tissues immediately under the hydatodes and over the terminal bundles, 
but after a few days or weeks they form a closed cavity in the heart of the leaf-tooth (fig. 11) 
and make their way into the spiral vessels under the epithem. Once established in the 
vascular system, they multiply with great rapidity, and their downward movement 
through the vessels of the leaf and into the main axis of the plant is then often only a matter 
of an additional week or two. 
Stomatal infections.—I will begin with the recently discovered black spot of the plum, 
to which I have thrice before called attention, namely, December 1902, December 1903, 
and December 1904, at meetings of the Society for Plant Morphology and Physiology 
*Fic. 11.—Water-pore infection of cabbage by Bact. campestre. The section is parallel to the surface of the leaf 
and passes through region of blackened leaf-tooth, the dotted part being that occupied by the bacteria. Collected at 
Jamaica, Long Island, N. Y., July 16, 1902. Slide 220 E7. 
