370 Scientific Proceedings, Royal Dublin Society. 



as they are threshed out of the bolls, to become contaminated with conidia. 

 Further, if the seed were at all damp, the mucilaginous nature of the outer 

 wall of its epidermis would, no doubt, assist in causing the conidia to adhere 

 to it. It was thought that this might possibly be the way in which the seed 

 carried the fungus, and it was therefore decided to contaminate seed with 

 conidia artificially, and to find out whether such seed, when sown, would give 

 rise to diseased seedlings. 



In the first experiment a quantity of flax-seed was divided into two 

 portions. One of these was steeped for one minute in sterile water, and was 

 then allowed to become air-dry. The other portion was steeped for a similar 

 period in sterile water containing Colletotricum conidia in suspension, prepared 

 by agitating diseased seedlings in the water. After these artificially contami- 

 nated seeds had become air-dry, both lots were sown in pots of soil which 

 were covered with bell- jars and placed in a greenhouse. 



At the end of ten days a good crop of seedlings had arisen in each pot. 

 The seedlings produced from the contaminated seed were in many cases 

 diseased, the fungus being identified with the microscope and found attacking 

 both the cotyledons and the stems of the seedlings. The seedlings derived 

 from the seeds steeped in sterile water showed no trace either of disease or 

 fungus. 



A second experiment of a similar kind was then undertaken. The conidia 

 used for preparing the steeping medium were, however, in this case derived 

 from a pure culture. The result was similar to the previous one. The con- 

 taminated seed gave rise to diseased seedlings, while the " control " seed 

 produced nothing but healthy plants. (See fig. 2, Plate XIX.) From the 

 diseased seedlings in this experiment Colhtotrichum linicolum was re-isolated 

 in pure culture by the usual methods. 



This experiment was repeated, a different sample of flax-seed being used. 

 One hundred artificially contaminated seeds gave rise to ninety-seven seed- 

 lings, seventy-eight of which were found to be diseased on the twentieth day 

 after sowing. In this case, however, out of the ninety-seven seedlings also 

 produced by the non-contaminated (control) seed, ten were found to be diseased. 

 This result was unexpected, and led us to suspect that the sample of seed 

 used in the experiment was already naturally contaminated with the fungus ; 

 and this was proved to be the case subsequently. 



In the next experiment, the seed used was first proved to be free from 

 natural contamination by sowing it and ascertaining that it produced nothing 

 but healthy seedlings. 



Four lots of this clean seed, of one hundred seeds each, were counted out 

 and steeped for one minute in a suspension of conidia (from a pure culture) 





