June IS, 1920 Relation of Rust in Seed Wheat to Seedling Infection 273 



section of a mature wheat kernel with telia upon the ventral surface. 

 Plate 45 is an enlarged portion of the same. 



Internal rust sori of wheat kernels were noted and described also by 

 Pritchard {22) . More recently CoUey {8) has listed 1 1 reports of internal 

 rust sori upon various hosts. He concludes that these are rather com- 

 mon teratological phenomena having no especial morphological signifi- 

 cance and can be expected to occur whenever the point at which the 

 sorus begins to form is located beneath a layer of tissue which is too 

 resistant for the sorus to break through. Plates 46 and 47 also show 

 internal sori. 



Histology of seedlings. — Rusted kernels of wheat were germinated 

 under various conditions and for various lengths of time. These were 

 fixed, sectioned, and examined for spread of infection from myceHum or 

 spores embedded in the tissues. Various materials were used for fixing 

 these young seedlings, but it was found that Juel's fixative penetrated the 

 embryonic parts better than any other which was tried, although Flem- 

 ming's medium fixative gave fairly satisfactory results. After section- 

 ing, either triple stain with excess of Orange G or Pianeze stain was 

 found to be satisfactory for differentiating host and fungus tissue. 



Infected seed was germinated under the following conditions. Seed 

 from lot I was germinated in compartments of an Altmann incubator 

 kept at 2°, 12°, and 17° C, respectively. Part of these were fixed when 

 the plumule was about ^ inch long, and the rest when the first leaf was 

 just beginning to unfold. Seed from lot 2 was germinated in com- 

 partments of the Altmarm incubator at temperatures of 2° alternated 

 with 17° and 11° alternated with 21°. The experiments with lots i and 2 

 were conducted twice — once in November, 191 5, and again in April, 191 6, 

 after the infected seed had been kept in a cool place over winter. Lot 

 3 was sown in pots which were placed in small chambers in the green- 

 house where the soil temperature was kept between 11° and 15° by the 

 use of ice. When the plants were about 3 or 4 inches tall they were 

 fixed, and a portion of each was sectioned and examined. Lot 4 was 

 germinated and buried out of doors in the ground at seeding time in 

 the spring. The plants were treated as were those in lot 3. 



Hundreds of sections were prepared from the material described above. 

 In no case was there any positive evidence of spread of infection from 

 the infected seed to the young plant. 



Plates 46 and 47 illustrate this fact. Plate 46 represents a longitu- 

 dinal section through a wheat embryo in a very early stage of develop- 

 ment. There is no indication of any spread of rust mycelium from the 

 sori seen in the infected hilar region at x. Plate 47 also represents a 

 longitudinal section of a wheat embryo. In this case development has 

 progressed considerably further than that shown on Plate 46. There is, 

 however, absolutely not the slightest indication of spread of rust myce- 

 lium from the large sorus shown at x. 



