i INTRODUCTION 7 



to an insufficient food supply, but it is also occasionally 

 due to excessive exposure to heat and sunlight. The 

 destruction or injury to the roots may be due to an 

 underground fungus or to some insect such as the grub 

 of a cockchafer biting through them ; again, it may 

 be due to their having reached poor soil, or having 

 exhausted most of the accessible nutriment. The 

 yellowing of the leaves is also noticeable in plants 

 growing in water-logged soil. 



When a plant is weak from insufficient food it is 

 much more liable to attacks from insects and fungi, and 

 where a plant has been injured by a pest, it is advisable 

 to manure it, so as to give it a fresh start and enable it 

 to resist the attacks of the pest. 



In the case of turmeric and ginger, the yellowing of 

 the leaf is a preliminary stage in the death of the leaf, 

 and is one of the signs that the plant is passing into 

 a resting stage. At this time the plant is ready for 

 digging, and the yellowing is therefore a normal con- 

 dition. 



INSECTICIDES 



Many different insecticides have been placed on the 

 market by horticultural firms. In most of them the 

 poisonous part consists of nicotine, or some form 

 of arsenic. Nicotine solutions are prepared by soaking 

 common or waste tobacco in water, enough being used 

 to cover the tobacco. When the solution is of the 

 colour of strong tea it is diluted and sprayed or watered 

 over the plants. Usually, in the East at least, tobacco 

 good enough for this purpose can be obtained cheaply. 



Arsenites of copper, Paris green and London purple 

 are often used, but I think it is better to avoid them, 

 as they are apt to burn the foliage, and there is a 

 probable risk of poisoning from them. 



Kerosene emulsion is one of the best insecticides, 

 It may be made with condensed or sour milk or with 

 soap, the latter being more generally used. 



