50 Forest Club Annual 



An experiment was performed to determine to some extent 

 the percentage of spores which fall during a rain and reach the 

 ground. During a very hard rain pieces of bark were nailed to 

 an upright board in the open. Sterile empty plates were exposed 

 below the cankers to catch the spores which fell with the rain 

 water. The contents of each plate were then centrifuged eight 

 minutes. The spores were precipitated into 1/10 cc. of water and 

 were placed under a cover glass. The total number of spores 

 collected in each Petri dish was then calculated. The Petri dishes 

 contained from 50 to 250 spores each, with an average of about 

 125 spores in each dish. This experiment showed that many 

 spores fall during a rain. All of the spores which fell could not 

 be collected because only one dish was exposed at a time. Rain 

 is instrumental in disseminating the spores through short dis- 

 tances, particularly washing them down from twig infections to 

 the lower parts of the tree. 



The solubility of the "spore horns" in water was shown by 

 spraying a chestnut branch bearing many threads of conidiospores 

 with distilled water. The threads of conidia disappeared with 

 surprising rapidity and by the time 10 cc. of water had been 

 used on the canker no threads were visible. The water was 

 collected in a crystallizing dish where the spores settled to the 

 bottom giving rise to a conspicuous clouded appearance in the 

 lower portion of the dish. 



In the work on the relation of air currents to the dissemina- 

 tion of the disease, an electric fan was used to produce a current 

 of air having a velocity of perhaps twenty miles an hour. The 

 air current was directed upon chestnut bark with threads of con- 

 idia projecting from the pycnidia. Tests were made with these 

 threads of spores dry, with them moist, and with the spray from 

 an atomizer playing over them, the last to imitate conditions pre- 

 vailing during storms. The spores were caught on the surface 

 of sterilized potato agar exposed about six inches from the bark. 

 Wet cotton was similarly held in the blast. It was then squeezed 

 out in distilled water which was centrifuged. The sediment was 

 used for a microscopic examination and the making of cultures. 

 There was unmistakable evidence, from each series of tests, 

 that the conidia may be detached by strong air currents and 

 carried short distances. The detachment was greater when the 

 spray from the atomizer played over the material. The results in- 

 dicated that the detachment was largely of small bits of the 

 tendrils composed of a great number of spores and that these 

 are too heavy to be carried to any great distance. Apparently, 



