388 Soil Factors on Disease Resistance 



The simplest explanation of these results appeared to be a fall in the 

 soil- temperature during the second half of October. That such a fall 

 actually does take place is proved by an examination of a set of soil- 

 temperature determinations made by Leake at Pemberandah in Bihar 

 in 1903-4. In the year in which Leake's readings were taken, the 

 Lathia amounted to 3-4 inches of rain and the daily soil-temperature 

 at 4 inches at 1-2 p.m., fell gradually from 29-5° C. on Oct. 16th to 

 22° C. at the end of the month. This disease of wheat seedlings, which is 

 very common in north-east India, is of some general interest, as the 

 Termites, although the apparent cause of the trouble, were in reality 

 engaged in the consumption of a moribund set of seedlings which had 

 been practically destroyed, apparently by a soil-temperature above the 

 maximum for growth. Examination of the root-system in this case 

 provided the clue which soon led to the discovery of the cause of the 

 trouble and to the working out of a simple remedy, which has since 

 been widely adopted on the indigo estates of this tract. 



The rust-resistance of einkorn 1 . Einkorn (Tritrium monococcum 

 vulgar -e Kche.) is well known to be exceedingly resistant to the attacks 

 of black rust (Puccinea graminis Pers.). In 1907, a plot of this wheat 

 was grown at Pusa when it was found to be immune to all the three 

 species of rust which occur in north-east India. The plants however 

 were still in the vegetative condition at harvest time and were allowed 

 to grow during the hot weather to see if any ears would form. No change 

 of this kind took place but early in May they were found to be severely 

 attacked by black rust. Here a prolonged rise of temperature led to the 

 complete loss of disease-resistance in a species considered to be immune 

 to this fungus. Unfortunately, the root-system at the time of the attack 

 was not examined, as the observations were made some years before 

 any attention was paid to such matters at Pusa. 



The various diseases referred to in this paper are considered to 

 establish a case for the detailed investigation of the root-systems of 

 plants, combined with a consideration of the chief soil factors, in con- 

 nection with the study of disease. There seems to be no doubt that the 

 conditions of the active roots profoundly affects the resistance of the 

 plant to the attacks of parasites. What this actually means in the pro- 

 cesses of metabolism is a matter for further investigation. The dis- 

 colouration and damage to the absorbing areas of the root are not 

 unlikely to lead to the entry of substances into the crude sap which 

 1 Journ. of Agr. Science, n, p. 278. 



