Oct. 21, i9i8 Angular-Leaf Spot of Cucumber 215 



Since the fruit invasions are local and shallow, it is evident that the 

 seed rarely, if ever, becomes attacked naturally. A study of the way the 

 seed is thrashed, however, sheds further light on the way in which the 

 seed may become contaminated. 



The thrashing process practiced on the farms visited is probably in 

 general use. It is begun by shoveling the whole fruits into a grinding 

 machine which chops them up and allows the larger parts of the fruit 

 pulp to be carried off on a rotating screen. The seed, the juice, and the 

 smaller pieces of pulp fall through the screen and are drained into con- 

 tainers. This much of the process would doubtless afford ample oppor- 

 tunity for the organisms to reach the seed. The next step, however, 

 probably increases the chances for the seed to become contaminated. 

 The seed with the pulp and juice is left in the barrels with frequent 

 stirring for a period of time varying usually from one to three days. The 

 angular-leafspot organism doubtless multiplies rapidly in this well 

 aerated mixture of juice and pulp unless conditions become unfavorable 

 owing to the by-products of other organisms. After the material con- 

 taining the seed has stood in the barrels for the time mentioned, it is 

 poured into other containers and the seed separated out as well as pos- 

 sible by repeated washings with water. Then the seed is dried on shallow 

 trays, at first in the sunlight and later indoors. The process of thrashing 

 includes no step v/hich would be likely to kill all the bacteria. 



Seed for further study was sent to Madison from both the Iowa and 

 Ohio farms. The details of some of the experiments performed with 

 this seed and the results are here summarized. 



Experiment OP February 20, 1917. — Sixteen flats of sand were steamed at 7 pounds' 

 pressure for one hour. Then each flat was planted with approximately 150 seeds 

 from Iowa. Before touching the seed the hands were rinsed in 70 per cent alcohol as 

 a precautionary measure. After the flats were planted they were wet down with 

 water that had been boiled (cooled), and boiled water was used in all subsequent 

 watering. None of the resulting seedlings were diseased. 



Experiment of March 3, 1917.^ — Fourteen flats of sand were steamed as before. 

 The hands were disinfected with mercuric chlorid and alcohol. Tne trowel was 

 treated with hot water. Twelve flats were planted with seed from the lot from Ohio, 

 about 100 seeds to each flat. One flat was planted with seed from the 1915 supply 

 which had been treated with i per cent formaldehyde for 20 minutes and another 

 with seed from the same lot which had been treated with i to 1,000 mercuric chlorid 

 for five minutes — ^these two for controls. The flats were covered with sterilized wire 

 screen to protect them from mice and rats. The flats were watered with water (cooled) 

 which had been boiled. 



On March 19 the writer found four seedlings in one of the flats showing typical signs 

 of angular-leafspot as they had been observed on seedlings artifically infected by plant- 

 ing inoculated seed and on naturally infected seedlings in the field (PI. 15, A). The 

 attacked seedlings were in two separated places — two affected seedlings next to each 

 other in each case — and apparently one seedling had been infected from its neighbor 

 in each instance. From a seedling from eachof thetwoplacesthe organism was isolated 

 and used in pure culture inoculations to reproduce the disease. Stained sections 



'Performed by Dr. M. W. Gardner in connection with his work on cucumber anthracnose. 



