brings into prominence certain other aspects which we must now 

 consider. We desire that the sum 



amx ny + cpz ..................... 



shall be a maximum while maintaining equality between -the values 

 ax, by, cz, ......... The latter desideratum requires further con- 



sideration in the light of what we have just said : this equality would 

 be necessary to maintain diversity if the country were uniform, but 

 it is not. The differences which exist between the various types of 

 cotton plant in their physiological response to environment render it 

 more than probable that, while ax may exceed by in one tract, the 

 reverse will be the case in another. Such considerations will lead 

 to the development of type tracts, and the equality indicated will 

 only develop a practical aspect in those border tracts where the type of 

 cotton to be grown will be determined by the extent of the demand 

 for the alternative classes of cotton these types produce and by the 

 area already under those types. We must, therefore, qualify our 

 earlier statement as to the need for equality in the value of the produce 

 from a unit area. This has no general, but rather a local, significance. 

 Reverting to the main problem, we have studied certain methods 

 which are directed to the end. They aim at the production of 

 increased yield by purification of the crop and by demarcation of type 

 areas ; at the production of increased price through development of 

 uniformity in the produce. We depend here on certain features of 

 the environment which are selective, that is, features to which the 

 different types react differently. There is, however, another series 

 of environmental phenomena which are hot to the same extent 

 selective ; of such a nature are the more important pests of t he 

 cotton plant, especially the boll worm. Again much importance has 

 rightly been attached to the height of the water table due directly 

 and indirectly, through the canals, to the rise of the Nile. Lastly, 

 there is that series of phenomena which we may include under the 

 general designation of cultural: the effect on yield of different spacings. 

 different methods of culture, and such like. With these questions, 

 beyond recognizing their importance and emphasizing the necessity 

 for making adequate provision for their study in any serious attempt 

 to face the cotton problem as a whole, we have no concern. It must 

 not be forgotten, however, that such problems can be approached 

 from both sides. On the one side is the plant, in the first case reacting 

 to an insect and in the second to physical condition of the environment ; 

 on the other is the insect and, within limits, a controllable pHysica] 

 state. Not only do the insect and the physical condition require 

 to be studied, but also the plant's reaction to these stimuli. In the 

 first case, concurrently with entomological investigation, which has. 

 among other facts, indicated the seasonal character of the epidemic. 

 efforts require to be made to break the present coincidence between 



