60 DISEASES OF CULTIVATED PLANTS 



destructive insects. In tropical countries the evergreen, 

 coriaceous leaves of many plants are attacked by truly 

 parasitic lichens that form flattened, porcelain-like crusts, 

 and when present in abundance prove injurious. 



Spraying with a strong solution of Bordeaux mixture 

 during the winter, when the trees are resting, completely 

 destroys all lichens and mosses present on the trees. Even 

 quicklime dusted on the trunk when wet from rain will kill 

 the lichens present to a great extent. 



Crown gall. This disease appears to be very prevalent 

 amongst fruit-trees of various kinds, also raspberries in the 

 southern and central parts of the United States. The 

 cause is not known, but some parasitic organism is suspected. 

 The disease is characterised by the presence of rough knots 

 or enlargements on the roots, usually just underground, but 

 often on the smaller roots lower down, less frequently on 

 the stem. The galls are distinguished from other similar 

 swellings by the rough warted surface and more or less 

 hemispherical form. On apples the galls are usually accom- 

 panied by a superabundance of fibrous roots. Such galls 

 prove injurious in several ways ; they interfere with the 

 conduction of water and food materials when they occur on 

 the main root, and they may cause the tree to produce fruit 

 too young, etc. It has been proved by careful experiments 

 that healthy plants of apple, peach, plum, and raspberry can 

 be infected with galls taken from other kinds of trees, show- 

 ing that the same organism is the cause of the disease on 

 different kinds of trees. 



The recommendations for its suppression are as follows : 

 Do not use seedling with 'hairy root,' or an excessive 

 development of fibrous roots, or with indications of 

 galls. In grafting, the disease may be communicated 

 from diseased to healthy plants by the knife. Gall is 

 more prevalent where the point of grafting is close to the 

 ground. 



Norton, J. B S., Maryland Agric, E%p1. Station, Circular 

 Bull. No. 56 (1904). 



Brunnisure. A disease of vine leaves both in Europe and 

 the United States ; has been described as due to an organism 

 named Plasmodiophora vitis (Viala and Sauv.). The Cali- 



