16 



bodied insects. It is one of the earlier insecticides, and is in- 

 creasing in popularity to-day. Some years ago its use was not 

 much recommended on account of the difficulty of preparing a 

 wash, etc., containing a given quantity of the active insecti- 

 cidal constituent, namely nicotine. At the present time, how- 

 ever, there are a number of extracts on the market in which 

 the proportion of nicotine is fairly constant, and by diluting 

 these a reliable wash can be obtained. The home-made wash 

 is very unreliable. It is usually prepared by soaking tobacco 

 stalks and waste in water, at the rate of one pound of tobacco 

 to one gallon of water, for several days. The water should not 

 be boiled, as this drives off some of the volatile nicotine, and so 

 weakens the wash. The darker and stronger the tobacco, the 

 better the wash. In South Africa tobacco wa.sh is recom- 

 mended for use against the following important insect pests 

 amongst others : Woolly aphis on apple trees, green aphis on 

 peach trees, black aphis on orange trees, cabbage aphis, black 

 peach aphis, bean and pea aphis and onion thrip. 



MOSAIC DISEASE. One of the most common diseases of 

 growing tobacco is called " calico," or " mosaic " disease, be- 

 cause of the mosaic-like appearance of the light and green por- 

 tions of the leaf. The disease causes the leaf to grow more 

 rapidly near the veins than elsewhere, and thus become 

 wrinkled and corrugated. A portion, or all of the plant, may 

 be affected. Slightly diseased leaves are worthless as wrappers, 

 and highly diseased leaves are of no value for any purpose. For 

 many years the nature of this disease has been a mystery, and 

 has been variously regarded as due to a fungus, as the result of 

 an excess or deficiency of minerals in the soil, as produced by 

 bacteria or induced by faulty drainage. Dr. Woods, of the 

 United States Department of Agriculture, who has carefully 

 investigated the disease, has arrived at the conclusion that it is 

 due to none of the generally supposed causes, but that it is 

 due to defective nutrition of the young dividing and rapidly 

 growing cells, due to a lack of elaborated nitrogenous reserve 

 food, accompanied by an abnormal increase in activity of 

 oxidising enzymes in the diseased cells." These are the same 

 enzymes that prove so beneficial in the fermentation process 

 later. The enzymes are liberated by the decaying plants or 

 roots, and, if in excess, may enter the roots of young plants set 



