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Dale. — A Bacterial Disease of Potato Leaves. 
Bacillus Solanacearum 
(Smith). 
28. — 
29. — 
30 - 
School of Agriculture, 
Cambridge. 
October , 1911. 
Bacillus melanogenes 
(Pethybridge). 
Produces enzyme capable of 
dissolving the middle lam- 
ella of cells. 
On sterile potato at 25 0 C. yel- 
low slimy growth is formed 
in 2 days. After 6 days be- 
comes brown. 
On living potato. Slight 
brown colour, later black. 
Middle lamella dissolved. 
Moisture needed. 
Bacillus Tubifex , n. sp. 
Produces enzyme capable of 
dissolving the middle lam- 
ella of cells. 
On sterile potato at 20° C. a 
dirty white slimy growth is 
formed, raised up into bub- 
bles. 
As B. melanogenes . Smells 
strongly ammoniacal on 
living potato. Goes brown. 
EXPLANATION OF FIGURES IN PLATES XV AND XVI. 
Illustrating Miss Dale’s paper on a Bacterial Disease of Potato Leaves. 
PLATE XV. 
Fig. 1* Surface view of the epidermis of a potato leaf, showing the bacterial infection tubes 
entering the tissues of the host through the cuticle and not through the stomata. The tubes are 
coloured red in all the figures. 4 oc. 2 mm. obj. (oil immersion). 
Fig. 2. Surface view of older stage to show the lumen. Note that the cell-walls on each side 
of both tubes are stained pink because they have been chemically altered by the parasite. 4 oc. 
2 mm. obj. 
Fig. 3. Another surface view of older stage with the end of the tube more thickened. 
4 oc. 2 mm. obj. 
Fig. 4. Transverse section of an epidermal cell and of adjacent cells, showing two tubes which 
are markedly thickened at the surface of the leaf. Note the prolongations above the surface in the 
left-hand tube and the lumen, and the dilatation where the right-hand tube pierces the cell-walls of 
the host. 4 oc. 2 mm. obj. 
Fig. 5. A young complete tube with a single narrow projection beyond the epidermis. The 
tube widens gradually with very irregular contours and shows several constrictions. Towards its 
inner end it becomes narrower, and there are traces of granular contents in the lumen. 4 oc. 2 mm. obj. 
Fig. 6. A short piece of a tube, shown where it crosses three cell-walls. The swellings at the 
points where the walls of the host cells are pierced is very marked. 4 oc. 2 mm. obj. 
Fig. 7. A portion of a tube to show the behaviour in an intercellular space. The surrounding 
cells are more or less diseased and contain some Bacteria. 4 oc. 2 mm. obj. 
Fig. 8. Two tubes in a later stage of the disease. These tubes anastomose and branch, ending 
in the phloem of a small vein. A few Bacteria are to be seen on the surface of the leaf near the 
outer ends of the tubes. One of the cells of the host, immediately below the epidermis, is filled with 
Bacteria and its chloroplasts are degenerating. The intercellular course of the tubes is very clearly 
shown in this section. 4 oc. D obj. 
Fig. 9. One tube is here seen branching and passing between the cells of the host into a small 
vein where some of the cells and vessels contain Bacteria. 4 oc. D obj. 
Fig. 10. This shows an unusually large number of tubes, in close proximity, in the neighbour- 
hood of a large vein. The tubes are seen at the surface, where each ends in several points. They 
have a more or less nearly straight course and are unbranched. Numerous cells containing Bacteria 
are also represented. Other examples, showing equally numerous tubes, were met with in examining 
series of microtome sections. 4 oc, D obj. 
