LEAF BLIGHT OF THE PEAR. 



sprinkled, remained alive till late in the autumn; and upon these I did not observe the 

 sulphur to operate in any degree, till the period at which the conic processes above men- 

 tioned would have appeared; but the yellow spots then became black, and perished, with- 

 out aflbrding seeds; whence I have reason to hope, that flour of sulphur will prevent, 

 in some measure at least, the rapid extension of this disease. 



" As the existence of this species of fungus appeared, three years ago, to be confined to 

 my garden and a few pear trees in its vicinity, and to the hawthorn in an adjoining hedge 

 (for it attacks the hawthorn as well as the pear tree,) I then thought it would be practi- 

 cable to ascertain decisively the means by which it transfers itself from one tree to anoth- 

 er: and this appeared to me to be an important object, because the habits of the Lycoper- 

 don canccllatam, and of the fungus which forms the rust or mildew of wheat, are, in 

 man}^ respects, very similar. 



" I had so often tried, without success, to transfer the mildew of wheat, and other 

 plants, from a diseased to a healthy subject, in the same season, that I had not any ex- 

 pectation of succeeding in an attempt of that kind ; but I thought it not improbable that 

 I might succeed in communicating this disease to seedling plants of the pear tree, having 

 long ago satisfied myself that the species of fungus, Arhich forms the mildew of wheat, 

 always rises from the root of the plant. 



" I have many years been in the habit of raising annually pear trees from seeds, with 

 the hope and expectation of obtaining new and hardy varieties; and as the means I em- 

 ploy to obtain seeds well calculated for my purpose, necessarily cost me a good deal of 

 time and labor, I have always planted them in pots, and in the kind of mould which long 

 experience has pointed out to me as the best. This I have always obtained, at the period 

 of sowing the seeds, in January or February, from the banks of a river at some distance 

 from my garden; and in this mould my seedling pear trees always sprang up, and re- 

 mained during the first season perfectly free from disease. In the spring of 1813, a por- 

 tion of this mould, which I did not want, was intentionally placed very near some haw- 

 thorns and pear trees upon which the Lycoperdon cancellatum abounded, where it re- 

 mained till the spring of 1814, when it was put into pots, and new seeds deposited in it. 

 These sprang up as usual, and remained in perfect health till the end of Mayor beginning 

 of June; when the fungus presented itself upon almost all the first true leaves of the 

 plants, which leaves had composed the plumules of the seeds. 



" That the fungus in this case rose from the ground, will, I think, scarcely be questioned ; 

 but it is necessary to state, that the seeds were all taken from trees which were not quite 

 free from disease, and that I saw in the last spring some diseased plants, in a case where 

 every precaution, except that of using new pots, (which had been my previous custom,) 

 had been taken; and therefore whilst so little is known respecting the habits of plants of 

 this tribe, the preceding facts are not sufficient to support a decision, that the source of 

 the disease might not have been in the seeds themselves. For as the fructification is pro- 

 bably every thing which is seen of this, and many other parasitical fungus plants, the 

 plant may extend in minute filaments through the whole body of the tree which sup- 

 ports it; and it appears in this view of the subject possible, that these slender filaments 

 may extend into the seeds. Tlie following circumstances, however, militate strorigly in 

 opposition to this conclusion. A great number of seedling pear trees, which were very 

 much diseased, were removed in the last spring, from my garden to a distant situation, 

 after having had their roots and stems carefully and repeatedly washed and brushed, so 

 remove from them every paiticle of the mould in which they had previously g: 

 on these not a vestige of disease has since appsared. Grafts also, which 



