EXPERIMENTAL PRODUCTION OF PARASITES. 43 
From other experiments the following general results were obtained: 
The variety Blanchard is very sensitive. Pousse Debout is very resistant. ‘Tubers of Chave 
from I and IV were most attacked, those from V least. Tubers of Chardon from IV were seriously 
injured, those from I and II only a little, and those from III not at all. In tubers from plots I and 
IV a black zone was observed between the attacked and the healthy tissues. As this stain was not 
noticed elswhere, Laurent attributed it to the nitrogenous product formed by the bacteria at the 
expense of the tissues. 
Corresponding experiments made at 20° to 22° C. on Simson and Chardon potatoes and chicory 
and carrot, gave very similar results. The inoculating material came from a third passage through 
Early Rose, and was, therefore, quite virulent. All tubers and roots from plot IV were rapidly 
attacked. The varietySimson was muchless resistant to this bacillus than to B. fluorescens putidus. 
Carrots from plots V and III and chicory from plots I, V, and III, resisted most strongly, while 
those from IV were always completely attacked. 
Comparative experiments were also made on tubers coming from (1) a field dosed with 800 kg. 
sulphate of ammonia, 800 kg., superphosphate, and 400 kg. each of kainite and sulphate of lime 
and (2) a field which had received 80,000 kg. of barnyard manure. Tubers from (1) rotted completely 
at 35° within 5 days after inoculation with virulent bacilli. Those from (2) rotted, but less rapidly. 
Tubers from unfertilized land resisted the rot better than either of the other lots. Hence, Laurent 
concludes that the use of fertilizers, by allowing an exaggerated. absorption of nitrogenous com- 
pounds, favored bacterial invasion. He states that lime diminishes the resistance of the potato, 
carrot, and chicory. Nitrogenous fertilizers and potash salts had analogous but less striking 
effects. On the other hand, phosphates, and to a lesser degree sodium chloride, increased the 
resistance. 
The results with lime led Laurent to believe that differences in resistance were due to a modi- 
fication in the acidity of the cell-sap. Experiments were undertaken to test this as follows: 
Tubers of Chave and Chardon, from plot III, known to be resistant, were cut in two and plunged 
for 5 hours in the following solutions made up with distilled water: 
Mbasartene Reto ate ose o5 555 Sas 39 oe FO ek isis cialerSieiet Alaa e sre Gah ae Stas BS Gaia Dare ears 2 per cent. 
MAMMA EETIW SELIDULO: A855 51 savas tees acs lo sravet elt acer ese ore atacs Fre aavakavoie NU lematar bg cole ay Haremavatee ouieal al I per cent. 
PUNMIOUIN SDHC. 5: 5id saneis oR oe Se ckhe 6 Tae de 585K Bon ahem aeag ees as ee 2 per cent. 
ROSIE LIBAN oh cI f5:ccevengia SiANe Cex CAT eae Glaser trent ovat rh Toayart ays ete ashaVEP SNE fb Anes eehe ath ona ce eros as 2 per cent. 
At the same time tubers of Early Rose and Marjolin from plot IV, known to be sensitive to 
rot, were similarly plunged in the following solutions: 
Netitral sndutm phospnate; sais. se. bes ba beecsts sua eeweeaeaemtrecae tas tents 2 per cent. 
Mecttral petaseni Phospnates: ¢s¢ 525.2.5.5.ac ki 0 Se wawlesee otis elses a aoenerepes toed mapas by 2 per cent. 
Prediral qremMontusa PhHOSpHate...6.¢ ccc aiscw cea oa cargpadioad s poe sete hts ONE bocey Ss 2 per cent. 
> All the tubers were inoculated with the bacillus from a fourth passage through Early Rose, 
and were kept in the thermostat at 35°. The first lot (resistant varieties) was uninjured, thesecond 
lot (sensitive variety) was attacked. Exposure to these solutions, therefore, did not alter the resistance 
of these varieties. Even exposure of the cut flesh of Marjolin and Blanchard for 40 hours to 1 per 
cent acid potassium phosphate did not protect them when inoculated; after 15 hours at 30° C. they 
were badly rotted. 
Resistant tubers of Chave and Chardon from plot III were immersed 3 hours in lime water, 
I per cent potash or 1 per cent soda solutions. At the same time sensitive tubers of Early Rose 
and Marjolin from plot I were plunged in 1 per cent solutions of tartaric, citric, and lactic acid. 
A)l were then inoculated with the bacillus from a fifth passage through Early Rose. After 12 hours 
at 35° all were infected; the alkalis rendered the resistant ones susceptible and the acids did not 
protect the sensitive ones. When the dose of organic acids was increased, however, the organism 
did not succeed in penetrating the tissues, the acidity of whose cell sap was thus artificially increased 
This is supposed to be due to the fact that the enzyme which dissolves the middle lamelle, acts 
on the potato only in a slightly acid or else in an alkaline medium. 
As shown above, the cut surfaces of resistant tubers were rendered sensitive by immersion in 
1 per cent alkaline solutions. The total acidity of the cell-sap does not, however, furnish an indica- 
tion regarding the mechanism of immunity, for tubers of Preciosa and Zeland, two refractory 
varieties, have an acidity (tested by phenolphthalein and estimated in milligrams of sulphuric acid 
per 100 cc.) expressed by 231.1 and 289.0, while Blanchard and Early Rose, two little resistant 
varieties, have an acidity represented by 317.8 and 387.1. 
Experiments were then made by immersing slices of little resistant varieties of potato for 12 
hours in the juice of two resistant ones obtained by great pressure (300 atmospheres) to test the 
protective effect of this juice. ‘The results obtained were somewhat contradictory. The juices 
