June 13, 1913] 



SCIENCE 



917 



made of the number of viable spores of the 

 blight fungus which were retained by each 

 trap. Traps were set at sis different locations 

 at West Chester, Pa., and analyses have been 

 made after each rain period for the months of 

 January to April, inclusive. 



There were seven rain periods in January 

 with precipitation varying from 0.13 to 0.88 

 inch. The number of viable pycnospores ob- 

 tained from each trap varied from 55,000 to 

 61,255,000 for each analysis. During Febru- 

 ary there were four rain periods with precipi- 

 tation varying from 0.07 to 0.78 inch. After 

 each rain the number of viable pycnospores 

 obtained from each trap varied from a few 

 thousand to 92,000,000. Similar results have 

 been obtained for the months of March and 

 April. 



The cotton for the traps was transported to 

 the laboratory in sterile Petri dishes and the 

 number of viable spores determined by the 

 iwured plate method, using 3 per cent, dex- 

 trose agar, plus 10. 



One of the noteworthy facts is that asco- 

 spores do not appear to be washed down the 

 tree during the winter rains, although they 

 are present in abundance in the pustules. 

 That all the colonies appearing in the poured 

 plates made from the cotton traps came from 

 pycnospores was demonstrated in two different 

 ways : first, by their time of appearance ; sec- 

 ond, by the absence of ascospores in the cen- 

 trifuged sediment as determined by micro- 

 scopic examination. 



The effectiveness of the cotton traps in re- 

 taining the spores washed down has also been 

 determined by cultures. In many cases only 

 about two per cent, of the spores passing into 

 the cotton was retained. This being true, the 

 figures given above are but a meager expres- 

 sion of the enormous numbers of pycnospores 

 produced. Considering the fact that we have 

 also demonstrated that pycnospores can be 

 subjected to freezing temperatures for consid- 

 erable periods without losing their vitality, 

 they must play a very important part in the 

 dissemination of the blight fungus. 



The forcible expulsion of the ascospores of 

 the blight fungus has been reported by Ran- 



kin" and Anderson' and the influence of mois- 

 ture upon this phenomenon has been demon- 

 strated by both writers. They have not, how- 

 ever, taken temperature conditions into ac- 

 count. The expulsion of ascospores depends 

 not only upon the presence of sufficient mois- 

 ture, but also upon the temperature to which 

 the lesion has been subjected. The influence 

 of temperature upon the expulsion of asco- 

 spores has been determined during the past 

 winter by means of laboratory and field tests. 

 Laboratory tests have shown that bark bearing 

 perithecial pustules, if subjected to low tem- 

 peratures (42 to 46° F.) for a period would 

 not begin the expulsion of ascospores until 

 exposed to favorable temperatures for three or 

 four days, even though supplied with an abun- 

 dance of moisture. The minimum tempera- 

 tures at which spore expulsion takes place 

 vary from 52 to 60° F. 



On November 26, 1912, a large number of 

 ascospore traps (49) were placed upon lesions 

 of the blight fungus in a badly diseased cop- 

 pice growth at West Chester, Pa. These have 

 been under continuous observation since that 

 time and accurate rainfall and temperature 

 records kept at that station. There was prac- 

 tically no expulsion of ascospores until March 

 21, although there had been many rain periods 

 (21) with precipitation varying from 0.01 to 

 1.64 inch. The above records show that asco- 

 spores were not washed down from the lesions 

 during any of the winter rains and that there 

 was practically no expulsion of ascospores 

 during the period from November 26 to 

 March 21. F. D. Heald 



M. W. Gardner 



Pennsylvania Chestnut Tree 

 Blight Commission Laboeatoet, 

 Philadelphia, Pa. 



a striking correlation in the peach 

 The importance of correlations in the char- 

 acters of plants from the standpoint of either 

 research or practise is so weU known as to 



' Eankin, W. H., Report Penna. Chestnut Blight 

 Conference, p. 46, 1912. Phytopathology, 3: 73, 

 1913. 



'Anderson, P. J., Phytopathology, 3: 68, 1913. 



