New York Agricultural Experiment Station. 235 



put into large pots in the cool greenhouse. They started up vigor- 

 ously and made most abundant and normal growth. No rust has 

 appeared on the plants up to the present time. They were kept 

 under constant observation and a careful study was made to deter- 

 mine if the plants harbored any viable urediniospores. The work 

 regarding the spores was in charge of Mr. Edward J. Petry, an instruc- 

 tor in the college and an unusually careful worker. He made an 

 examination to ascertain if urediniospores were still harbored on 

 the currant canes. It was assumed that they might be caught in 

 the axils of buds and branches, on the scales or the fascicled bases 

 of the stems. Several plants were carefully washed in order to 

 secure all the spores which were attached. Eighty cubic centi- 

 meters of water was used at each washing and this was centrifuged 

 in eight tubes. One-half cubic centimeter of sediment was taken from 

 the bottom of each tube and placed on several young leaves which 

 were carefully marked. This was repeated twice at different later 

 stages of development of the leaves. No infection has occurred up to 

 the present time. Mr. Petry made an estimate of the number of 

 spores placed on the leaves as follows: 'From careful quantitative 

 counts under the microscope, \ c. c. at the bottom of each tube con- 

 tained 100 spores, i. e., 1/40 c. c. approximately was used in each count, 

 and ten counts were made for one tube of each washing (which had 

 been thoroughly shaken up before centrif uging) . The counts of 

 the spores ran from 2 to 7 spores, i. e., an average of 5 spores per 

 count was found. This would make 5 x 20 (\ c. c.= 20/40 of 1 c. c.) 

 or 100 spores per | c. c. This \ c. c. (containing probably 100 spores 

 or more) was placed on 5 leaves so that each leaf should have received 

 20 spores and if these spores were at all viable, infection should 

 have taken place. Some leaves were given \ c. c. in different drops, 

 but neither these nor the others showed infection. In all, about 

 100 leaves were tried, but none showed signs of infection. From 

 the above data, there must have been upwards of 2,500 spores in 

 all these centrif ugings.' 



"I saw quite a number of slides from this centrifuge material. 

 The urediniospores were abundant, but I saw none which appeared 

 to me to be certainly viable. I am inclined to think from this work 

 that if urediniospores remain thru the winter in condition to start 

 infection the following spring it must be under exceptional circum- 

 stances. I am inclined to think that such result does happen occa- 



