40 MASSACHUSETTS HORTICULTURAL SOCIETY. 



sown in the morning germinate more quickly and abundantly tlian 

 those sown in the afternoon. It was not possible to keep the spores 

 which were fonned in the night until the afternoon, as they gene- 

 rally fell from their attachments in the morning and began to ger- 

 minate. In all cases the germination took place with surprising 

 regularit}'. At the expiration of an hour and a quarter the contents 

 of the spores had formed small oval l^odies, which, before long, rup- 

 tured the cell wall and made their escape from the mother cell. 

 They passed out rather slowly, usually one at a time, and paused 

 for a moment in front of the opening, where they remained as if not 

 quite free one from another. In a short time, each body began to 

 extricate itself from the common mass, moved more and more ac- 

 tively, and finally darted off with great rapiditj^ — a full-fledged zoo- 

 spore, furnished with two cilia. The average number of these rap- 

 idly-moving spores is from six to eight. Their movement gradually 

 grows slower, and in from fifteen to twenty minutes they come to 

 rest. Soon an outgrowth proceeds from one side and rapidly devel- 

 ops into a new plant. The sexual spores are found in autumn, 

 within the tissue of the shrivelled leaves, as spherical, thick-walled 

 bodies. They escape by the breaking up of the diy leaf, or through 

 the decay of the surrounding tissue. The statement is often made 

 that the mildew does not grow on the Vitis vinifera. By carefully 

 conducted experiments. Dr. Farlow found it could be made to grow 

 on the leaves of this European species, and with the usual luxuri- 

 ance. 



The Black Knot, to quote from Dr. Farlow's excellent article on 

 this subject, published in the " Bulletin of the Busse}^ Institution,'' 

 Vol. I, p. 440, is " without doubt the most striking disease of veg- 

 etable origin occurring on fruit trees in this country. The disease 

 takes its name from the unsightly, black, wart-like excrescences, with 

 whicli ever}' one is familiar on plum trees and different kinds of wild 

 and cultivated cherries. It is found in all parts of our country, 

 east of the Rocky mountains, and is so common and destructive that 

 in some districts one seldom sees a plum tree free from the knot. 

 In some parts of New England, })articularly in Maine and along the 

 sea-coast, the raising of cherries has also been almost abandoned 

 in consequence of the ravages of the black knot. The disease is 

 peculiar to America, and has been the bane of fruit-growers from 

 earl}' times ; and allliough much has been written in agricultural 

 papers about its inju iy to the fruit crop the subject has been almost 



