June IS, 1920 Relation of Rust in Seed Wheat to Seedling Infection 267 



EXPERIMENTAL DATA 



It is seen from the foregoing review that a number of workers have 

 grown rust-infected seed grain under various degrees of isolation and with 

 more or less conflicting results. The evidence of this kind as to the trans- 

 mission of Puccinia graminis by means of seed seems to be largely nega- 

 tive. Nevertheless some positive results have been reported. The one 

 conclusive way to prove the contention that rust can be carried on seed 

 grain must be to produce the disease upon plants grown under controlled 

 conditions from seed known to be infected with the rust. While histo- 

 logical evidence is valuable from the standpoint of interpretation, yet no 

 amount of such work by itself is fully convincing in connecting seed in- 

 fection wdth the appearance of the disease upon the leaves unless plants 

 can be grown from infected seed under controlled conditions and the dis- 

 ease be produced upon these plants. The writer's experimental investi- 

 gations were along three lines: (i) Greenhouse experiments in which 

 rusted kernels of wheat in large num.bers w^ere sown under isolated con- 

 ditions and the resulting plants watched for infection; (2) field experi- 

 ments in which rusted wheat kernels were sown in the fields and watched 

 to learn if infection occurred upon the resulting plants sooner than upon 

 plants grown from clean seed; and (3) histological investigations in 

 which rusted wheat kernels were germinated under various conditions 

 and the resulting seedlings examined histologically for spread of rust 

 infection from the kernel to the seedling. 



greenhouse; experiments 



The writer determined to test this matter thoroughly by growing a large 

 number of wheat plants from kernels known to bear sori of stemrust, 

 under conditions of isolation and at the same time under conditions 

 normal for the development of the host. In order to meet these require- 

 ments a room in the pathological greenhouses at the University of Wis- 

 consin was equipped as shown in Plate 40. The room was examined 

 carefully and every crack and opening sealed. Double doors were con- 

 structed with a space between, which could be sprayed each time before 

 the room was entered. An adjustable shade was placed upon the roof 

 in such a way that a spray of water could be thrown upon the glass 

 underneath the shade to aid in cooling the room, and a system of forced 

 circulation of washed air was installed, as shown in figure i. Thermo- 

 graph and hygrograph records were kept at all times when the plants 

 were growing, and it was found easily possible to control the temperature 

 and humidity within normal limits for growth of wheat plants. Plants 

 grown in this house were entirely normal in appearance and produced 

 plump kernels in every head. The accompanying photographs (PI. 41) 

 taken at different times during the period when the experiments were 

 in progress, show the normal, healthy condition of the plants. In 

 order to test the efficacy of this air-washing apparatus, about a pint 



