DISEASES OF PLANTS. 333 



the cells of the leaves and the tubers, and thus accelerating their de- 

 struction. Berkeley, Morren, and Townley, consider the Botrytis as 

 the cause of the disease. Various species of Botrytis also attack the 

 Tomato, Beet, Turnip, and Carrot. A species of Depazia sometimes 

 causes disease in the knots of Wheat. A diseased state of Rye and 

 other grasses, called ergot, owes its production to the presence of a 

 species of Spermoedia. By the action of the fungus, the ovary becomes 

 diseased and altered in its appearance, so as to be dark-coloured, and 

 project from the chaff in the form of a spur. Hence the name spurred 

 rye. The nutritious part of the grain is destroyed, and it acquires 

 certain qualities of an injurious nature. Spontaneous gangrene is the 

 consequence of living for some time on diseased rye. Ergot has been 

 seen in Lolium perenne and arvense, Festuca pratensis, Phleum pra- 

 tense, Dactylis glomerata, Anthoxanthum odoratum, Phalaris arun- 

 dinacea, &c. 



697. Fruits when over-ripe are liable to attacks of Fungi, which 

 cause rapid decay; wood also, especially Alburn virn or sap-wood, is 

 injured by the production of Fungi. Dry rot is the result of the 

 attack of Merulius lacrymans, which in the progress of growth de- 

 stroys its texture, and makes it crumble to pieces. Some kinds of 

 wood are much more liable to decay than others. 



698. The diseases caused by attacks of Fungi may be propagated 

 by direct contact, or by the diffusion of the minute spores through the 

 atmosphere. When we reflect on the smallness of the spores, the 

 millions produced by a single plant, and the facility with which they 

 are wafted by the wind in the form of the most impalpable powder, 

 we can easily understand that they may be universally diffused and 

 ready to be developed in any place where a nidus is afforded. Perhaps 

 some of the diseases affecting man and animals may be traced to such 

 a source. Quekett found that he could propagate the ergot by mix- 

 ing the sporules with water, and applying this to the roots. 



699. In order to prevent these diseases, it has been proposed to steep 

 the grains in various solutions previously to being sown. For this 

 purpose, alkaline matters and sulphate of copper have been used. In 

 all cases, the seed should be thoroughly cleansed. Smut and pepper- 

 brand have been averted by these means. In the case of the latter, 

 diseased grains are easily removed by being allowed to float in water, 

 and the grains that remain are washed with a solution of lime, com- 

 mon potash, or substances containing ammonia, which form a soapy 

 matter with the oil in the fungus. A weak solution of sulphate of 

 copper acts by destroying the fungus. To prevent wood from dry rot, 

 the processes of kyanizing and burnetizing have been adopted: the 

 former consists in making a solution of corrosive sublimate enter into 

 the cells and vessels; the latter, in impregnating the wood with a 

 solution of chloride of zinc. Creosote has also been used to preserve 



