590 \ r A I . F ( )l^ M A T 1 \ S A X T) }^ I S K A S E S 



fill soil, than on those which are reared in good garden land. 

 The blight also in Wheat, which is a degeneration of the 

 "Tain, bj vhich it passes into Coniomvci, seizes for the most 

 part on grains tiiat are not ripened, btit not on those that have 

 attained their perfect state. VVe can hence partly provide 

 against the occurrence of this disease, by permitting the seed 

 to become pei-fectly ripe and hard before it is taken in ; and 

 even then it ought not to be stacked, but instantly thrashed 

 out to such an extent, that only about two-thirds of tlie grain 

 may be beaten out, and the less ripe seeds left behind. 



That a diseased tendency must, for the most part, pre- 

 viously occur, when diseases are generated in plants, even 

 by parasitic plants, is evident from the growth of Fungi 

 on sickly stems and branches. On our Alder we find the Bo- 

 letus alneus ; on our Willow, Boletus adustzis, fumosuSy and 

 suaveolens ; on our Beech, Boletus fomentarms ; on our Birch, 

 Boletus hetulinus ; on our Ash, Boletus Jraxineus ; and on 

 the stem of the Oak, Dadalca quercinay — as proofs of the 

 diseased state of the plant, and of the tendency of its juices^ 

 to corruption. In like manner, a number of Fungi, as al- 

 so the RMzoviorpha suhcorticalisy appear upon the roots of 

 trees when they stand in too moist a soil, shewing the diseased 

 disposition of the roots. 



419. 



The barks of our trees are subject to cracks, to the flowing 

 of resinous matter, to leprosy, and seal), — all of which dis- 

 eases either pass into others that are still more dangerous, or 

 invite a crowd of parasitic plants and insects, by which the 

 evil is made worse. 



The cracking of tliC bark in our fruit trees is for the most 

 part the consequence of an over luxuriant growth, during which 

 too many layers of alburnum are deposited, so that the inner 

 bark and the rind cannot yield and make room for them. 

 The inner bark being thus rent, usually makes way for the 

 passage of the nutritive sap through the rent, and this sap, 

 when it reaches the air, assumes the consistence of gum. By 

 this means the tree must naturally be enfeebled, and finally 



