DISEASES OF PLAl^'TS. 401 



rapid decay. Wood also, especially alburnum or sapwood, is injured 

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

 Meruleus lacrymans, which in' the progress of growth destroys the 

 texture of the wood, and makes it crumble to pieces. Some kinds 

 of wood are much more liable to decay than others. Peziza Eeru- 

 ginosa, which grows on the dead branches of oak and larch, imparts a 

 verdigris colour to the wood. 



The diseases caused by attacks of Fungi may be propagated by 

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

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

 millions produced by a single plant, and the facUity 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. Diseases of the skin are often aggravated by attacks 

 of Fungi. This is the case in the disease called Porrigo. Diseases 

 in animals, such as the silkworm and polistes, are caused by Fungi. ^ 



Mr. Lawes observed a luxuriant growth of Fungi on wmmanured 

 plots of ground, and in plots receiving mineral without nitrogenous 

 manure; and by far the most vigorous growth of grass on " fairy rings " 

 was on superphosphated plots, and those receiving superphosphate with 

 salts of soda and magnesia, without potash. Ammonia salts seem 

 to prevent the growth of Fungi. Fairy rings occur most abundantly 

 in poor pastures, and one mode of extirpating them is the application 

 of nitrogenous manures. 



In order to prevent fungoid diseases, it has been proposed to steep 

 grains in various solutions previously to being sown. For this pur- 

 pose alkalin^ 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. Diseased grains may be 

 removed by being floated off in water, and the grains that remain 

 may be washed with a solution of lime, common potash, or sub- 

 stances containing ammonia. A weak solution of sulphate of copper 

 acts by destroying the fungus. To preserve 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. Creasote has also been used to preserve 

 wood. Boucherie proposed that a solution of pyrolignite of iron 

 should be introduced into trees before being felled, by making perfora- 

 tions at the base of the trunk, and allowing the absorbing power of 

 the cells and vessels to operate. This plan does not appear to have 

 been successful, although it was reported on favourably to the French 

 Academy. 



2d 



