VARIETAL RESISTANCE 285 



the whole appears to exhibit a tendency to be correlated with 

 short staple. 



A further step was taken when the Cambodia variety of resistant 

 cotton, introduced into India a number of years ago from French 

 Indo-China, was tested out under South African conditions. 

 This variety has also the definite property of hairiness and, 

 according to Parnell (1925), it was found to show immunity — the 

 jassid does not appear to breed upon it or injure it in the least 

 degree. The large size of the plant, and its rather weak and 

 delicate stems, which render it susceptible to storm injury, make it 

 of doubtful promise as a field crop. Only further work will show 

 whether it is possible to obtain less rampant strains. At the same 

 time, research is being carried out with the object of selecting and 

 testing promising local varieties betraying evidence of jassid- 

 resistance in the field. In the latest available Report on the 

 subject, it is stated that remarkable progress has been made in 

 this direction and has resulted in the discovery of several strains, 

 of which those known as Z.l and U.4 are both highly resistant to 

 jassid attack, of good staple and prolific yielders. This has led 

 to supplies of their seed being sent to farmers, and to an increase 

 of acreage given over to cotton-growing. It would appear that 

 the discovery of these resistant varieties has brought the solution 

 of the problem within sight. Doubtlessly, much further work is 

 still necessary with regard to re-selection and improvement of 

 these types, and it remains for the future to show whether their 

 inherent properties will be retained under diverse local conditions. 

 Their discovery, under the aegis of the Empire Cotton Growing 

 Corporation, is one of great importance, and will lend encourage- 

 ment to further efforts in the same direction, with reference to 

 pests in other parts of the world. 



