44 BACTERIA IN RELATION TO PLANT DISEASES. 
tested were boiled and unboiled. ‘They were exposed to the oxydizing action of the air. The 
slices of potato after exposure for 12 hours in these juices were inoculated with pulp from a rotting 
tuber. Blanchard and Early Rose rotted readily. Simson exposed to the juice of Zeland rotted 
some, Simson exposed to the juice of Preciosa (cooked and uncooked) did not rot. Zeland exposed 
to the juice of Preciosa (cooked and uncooked) did not rot. Zeland exposed to its own juice (raw) 
lost its natural immunity and rotted, but resisted after exposure to its own juice cooked. ‘The most 
interesting result is the supposed immunity acquired by Simson on soaking in the juice of Preciosa. 
(This conclusion seems to have been based upon a single experiment.) 
His general conclusion is that the resistance of potato tubers is due to the existence of some 
soluble substances in the cell-sap, the réle of which can be destroyed by alkaline solutions. The 
total acidity of the juice of the tubers doesnot correspond to theaction of these protecting substances.* 
The bacillus in question, i. e., that identified as B. coli, is very widely distributed, rarely capable 
of living parasitically on tubers of potatoes, and then only when the tubers have been deprived of 
resistance by exceptional cultural conditions. Its virulence varies greatly under different condi- 
tions. In no case were infections secured on normal tubers or roots when the inoculation material 
was taken from artificial cultures, even a passage through a slice of cooked potato suffices to suppress 
the parasitic tendency. The virulence does not continue to increase after 5 or 6 passages through 
raw potato. Laurent gives a list of 30 compounds from which this organism was able to take its 
carbon food, and a list of 14 from which it could not obtain carbon. 
‘Tous les mélanges organiques que je viensd’énumérer, et dans lesquels le bacille s’est développé, 
ont été déposés en quantité notable a la surface de tubercules de Marjolin coupés en deux, et légére- 
ment excavés afin d’empécher le liquide ensemencé de tomber. Pour beaucoup de solutions, les 
essais ont été répétés plusieurs fois en variant les concentrations. Jamais le bacille ainsi cultivé ne 
s'est développé sur tubercules vivants qui n’ avaient subi aucune préparation spéciale. 
“Mémes résultats lorsqu’ aux tubercules de Marjolin, on a substitué ceux de variétés Early Rose 
et Blanchard, cependant si peu résistantes.”’ 
As already stated, the result was quite otherwise when portions of these cultures were placed 
on the cut surface of tubers previously treated with 1 per cent caustic soda or potassa. 
Light lessens the virulence: Thus tubers of Marjolin inoculated with bacilli from the thirteenth 
passage, placed under a bell-jar in the sunlight, remained intact even after the cultures were 
replaced in the thermostat. 
Heat beyond a certain point diminishes and even suppresses the virulence. Heating for 10 
minutes at 45° and 50° does not retard development, but when 55° and 60° of heat were used, the 
small colonies which started growth soon ceased to grow and the tuber healed. The bacillus, how- 
ever, can not attack the potato at a temperature of 40° C., although it grows up to 45°. 
Passage through different kinds of roots decreases the virulence. Thus after passing through 
the acid media afforded by turnips, radishes, or onions, the bacillus seems unable to secrete the 
alkaline substance necessary for the destruction of the middle lamellz of potato. 
Inoculations on various plants, roots, stems, and fleshy leaves gave slight development only 
around the point of inoculation. In the inoculated Opuntia, however, large brown, decayed spots 
appeared and the whole plant was finally destroyed. 
A section through a diseased tuber showed between the pulp and the healthy tissues a zone 
free from bacteria yet beginning to disorganize. This was due probably to secretions from the 
bacteria. 
*Averna-Sacca, who studied in Italy (St. Sp. Ag., 1910) the resistance of grape leaves to Oidium, Peronospora, 
and Erinose found the more resistant sorts had the greatest acidity of cell-sap. The acidity of the leaves expressed 
in terms of tartaric acid was as follows: 
Sorts. Per cent of dry weight. 
Average of 19 resistant varieties (Rupestris, Riparia, Berlanderi)................ 6.565 
Average of 31 non-resistant varieties (mostly European sorts).............00005 1.372 
An examination of the acidity of the must gave equally striking results: 
Grapes tested. Per cent of acid in the must. 
Average of 7iresistant American varieties .32.)sc035 3 a5,i da ins watieiaeeniedas ready 20.811 
Average of 10 non-resistant European varieties... 0.2.0.0... .0c cee c eee tee e teens 7.895 
On a field rich in lime these diseases were more prevalent than on a sandy loamy field and the quantity of acid 
in vine leaves from the sandy field was double that in leaves from the other field. 
The author’s conclusions are: (1) The resistance of the grape vine to the attack of parasites must be ascribed to 
the acidity of the juice of their organs: (2) This resistance is not stable but may undergo changes with cultivation or 
even be annulled completely, wild varieties being most resistant. 
