DISEASES OF CULTIVATED PLANTS 505 



on the under side are coated with a thick felt-like covering, which, 

 at first pure white, gradually turns rusty and finally becomes dark 

 brown. Generally, the swellings and corresponding depressions are 

 isolated and few in number on the affected leaves, but in severe cases 

 they are numerous enough to become confluent, and the whole lower 

 surface is then completely hidden by the felt-like covering. Occa- 

 sionally, indeed, the felt-like material extends to the upper surface 

 in narrow strips bordering the veins, and may even be found on the 

 petioles and flower clusters. 



Most of the specimens received at the laboratory were sent 

 under the impression that they were attacked by a fungus, and, in 

 fact, the coating has a strong superficial resemblance to some fung- 

 ous growths. A microscopic examination shows, however, that it 

 consists of a mass of hypertrophied hairs or abnormal outgrowths of 

 the epidermal cells of the leaf. They are larger, more abundant, and 

 more persistent than the normal leaf-hairs of the leaf, and differ 

 also in being often branched and usually unicellular. This ab- 

 normal growth, in common with similar growths found on other 

 plants, is called an erineum, from a Greek word meaning woolly. 

 This is the derivation of the word Erinose, which means woolly dis- 

 ease, a very appropriate name. The erinea of leaves were formerly 

 supposed to be of fungous origin, but are now known to be due to 

 the attacks of minute mites. The stings or punctures of these mites 

 exert a stimulating effect upon the epidermal cells of the leaf, which 

 causes them to grow out into the abnormal hair-like processes al- 

 ready described. 



Since sulfuring the vines for the treatment of oidium has be- 

 come general in France there has been little trouble with erinose. 

 The phytoptus seems as sensitive to the fumes of sulfur as the red 

 spider, and several sulfurings during the late spring and early sum- 

 mer are recommended for the control of the mite. The only vine- 

 yards which have been found badly affected in California are those 

 in which little or no sulfuring has been done, or those where the 

 growth of foliage has been so luxuriant as to prevent the evaporation 

 of the sulfur by the sun. In the latter cases the vines are so strong 

 that they practically receive no harm from the disease. In severe 

 cases a winter treatment of the vine stumps is practiced in France. 

 This treatment consists in pouring about one quart of boiling water 

 over the stump. For very large stumps a somewhat greater amount 

 of water is used, and for smaller vines a proportionate amount. 

 This method is said to be very efficacious, and with the portable boil- 

 ers constructed for the purpose two men can treat from 1500 to 2000 

 vines per day. Cuttings taken from affected vines for the purpose 

 of rooting or grafting may be thoroughly disinfected by placing 

 them in hot water (122 F.) for ten minutes. If this is done care- 

 fully all the mites and their eggs will be destroyed without injury 

 to the cuttings. (Cal. E. S. B. 136.) 



Necrosis of the Grape Vine. There are many signs by which 

 the disease may be recognized in the field: 



