Communications. 297 



related species, flourisbes best in moist, warm weather. Under 

 the microscope, the tissue of the grape leaf is seen to contain an 

 abundance of minute threads, which force their way in all direc- 

 tioDs between the cells of the leaf, thrusting their suckers into 

 the cells to rob them of their nourishment. When the time for 

 fruiting comes, the threads pass out of the stomata of the leaf 

 and branch in a definite manner, and bear the asexual spores on 

 their tips, as we have observed in the potato rot. Under the head 

 of the germination of these asexual bodies, Dr. Farlow has per- 

 formed some interesting experiments. He finds they germinate 

 equally well in the dark as in the light. Those sown in the 

 morning germinate more quickly and abundantly than those sown 

 in the afternoon. It was not possible to keep the spores which 

 were formed in the night until the afternoon, as they generally fell 

 from their attachments in the morning and began to germinate. 

 In all cases the germination took place with surprising regularity. 

 At the expiration of an hour and a quarter the contents of the 

 spores had formed small oval bodies, which, before long, ruptured 

 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 

 actively, and finally darted ofl with great rapidity — a full-fledged 

 zoospore furnished with two cilia. The average number of these 

 rapidly-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 develops 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 dry leaf, or through the decay of the surrounding tissue. 

 The statement is often made that the mildew docs not grow on the 

 Vitis viniftra. By carefully conducted experiments, Dr. Farlow 

 found it could be made to grow on the leaves of this European 

 species, and with the usual luxuriance. 

 . The Black Knot, to quote from Dr. Farlow, is " without doubt 



