THE NEW FORESTRY. 1 97 



The diseases and parasites, of one kind or another, that 

 attack trees are, according to investigators, so hopelessly over- 

 whelming in number that one is almost tempted to think they 

 are but a part of the " universal plan " in the economy of 

 nature, and need not be regarded in all cases as seriously 

 destructive agents. 



A list of the pests that beset but two of the best known 

 species, the oak and the Scotch fir, for example, will afford 

 some idea of the nature of the task anyone has before him who 

 regards them as troubles calling for practical measures of 

 prevention or cure over large areas The oak and Scotch fir 

 happen to be among the worst afflicted, it is true, but their case 

 is suggestive. According to Schlich, Kallenbach, in an incom- 

 plete list, enumerates five hundred species of insects alone that 

 attack the oak ; while Hartig, in his " Classified List of 

 Diseases," resulting from cryptogams, phanerogams, bacteria, 

 and fungi, puts the number for the oak at fifteen. Nearly a 

 score of grubs and insects, etc., attack the Scotch fir, and 

 Hartig's number of diseases for the same tree is thirty, and so 

 on, Hartig's general list occupying twelve pages ; while he 

 states elsewhere that the predisposing causes, alone, of disease 

 are " endless." Another emphatic statement, of Hartig's, 

 p. 1 6, will bewilder those writers on forestry and gardening 

 who have so confidently held that disease is transmitted by 

 seed, and that, hence, seed should not be collected from 

 diseased trees and plants. Hartig writes, " a transmission by 

 inheritance of disease to descendants is unknown in the vege- 

 table kingdom. One may without hesitation make use of the 

 seeds of plants suffering from any conceivable disease for the 

 propagation of new plants." Hartig's definition of actual 

 disease is a " sickly condition leading to the death of some 

 part of the plant." A diminution of growth may not be 

 disease, but disease may result from it. According to the 

 general definition, disease is anything, excepting accidents, 

 that causes " a diminution of the functional power," and 

 Dr. Lindley, in his " Theory and Practice of Horticulture," 

 says the assertion that seeds in all cases produce healthy 

 plants will not bear exact investigation, and most foresters and 

 gardeners will agree with him. It is a general rule, says 

 Dr. Lindley, that seedlings take after their parents, an 

 unhealthy mother producing a diseased offspring, and vice 

 versa. There cannot be found a gardener of any large experi- 

 ence, he adds, who does not know that seedlings will exhibit 

 every diversity of constitution from health to decrepitude. 



