248 A neio Disease of the Plum. 



it were puffed up with air, being filled with an elastic spongy- 

 substance of a whitish color. In some of these inflated 

 plums no vestige of a kernel remained ; in others, a little, 

 soft, and empty shell was found. After growing from one 

 half to more than three quarters of an inch in diameter, the 

 fruit dropped, and by the middle of June no more of it was to 

 be seen on the trees. 



The cause of this puffy swelling of the fruit, and abortion 

 of the kernel, is a little tlirips; and several of these minule in- 

 sects were found, on the 2Sth of May, on almost all the dis- 

 eased plums. It is probable that they begin their attacks in 

 the blossom, and that they prevent the impregnation of the 

 ovule or young kernel, by destroying the pollen; and, by sub- 

 sequently puncturing the plum, produce an irritation, which is 

 followed by a rapid swelling and diseased condition of the 

 fleshy substance of the fruit. Preternatural enlargements and 

 distortions of the parts of flowers and of fruits are known to be 

 occasioned by the attacks of other species of tlirips. This 

 may be seen in the blossom of the black whortleberry, (Vac- 

 cinium resinosum;) all parts of which, calyx, corolla, stamens 

 and ovary are sometimes enormously enlarged, and entirely 

 changed in texture and appearance, in consequence of the 

 punctures of a kind of tlirips. 



It is not yet known how far this affection of the plum has 

 extended. In this vicinity it seems to have been confined to 

 certain trees only. Should the insects multiply and spread to 

 other trees and other places, they will prove very destructive 

 to the fruit hereafter. It remains, therefore, for the practical 

 gardener to watch for their first appearance, and to devise 

 some sure means of killing them, while the trees are in blossom 

 and the fruit is forming. T. W. H. 



Cambridge, June, 1842. 



We invite the attention of our readers to the above. New 

 insects and diseases appear to be upon the increase, and it be- 

 comes the intelligent cultivator to watch attentively for the 

 causes which produce such dire effects on his fruit trees. We 

 trust we shall be able to offer other communications from 

 Dr. Harris, on the habits of the various insects which annoy 

 trees and plants, and thus be the means of leading to dis- 

 coveries for extirpating them. — Ed. 



