Pethybridge and Lafferty — A Disease of Flax Seedlings. 371 



in sterile water. The four lots of seeds were then sown in separate pots at 

 varying depths below the surface of the soil. This was done in order to ascer- 

 tain whether there would be any correlation between the incidence of disease 

 and the carrying above ground of the seed-coats. The deeper the seeds were 

 sown, the less chance there was of the seed-coats being carried up. 



The results of the experiment are summarized in the following table : — 



It is clear that there is a close correlation between the carrying up of the 

 seed-coats and infection with the disease, but it is also clear that such carry- 

 ing up of the seed-coats is not absolutely necessary for infection, for in three 

 cases infection occurred, although the seed-coats remained in the soil ; and 

 further cases of this kind have been noted from time to time with naturally 

 infected seed. 



The foregoing experiments show clearly that the disease can be transmitted 

 by conidia adhering to the seed ; but they are, of course,' open to the objection 

 that the artificially contaminated seed was sown very soon after having been 

 prepared, and it does not therefore follow that this is the actual mode of 

 transmission which occurs in nature. 



Attempts were next made to discover conidia adhering to the seeds in 

 naturally infected samples, that is in those which gave rise to a certain 

 proportion of diseased seedlings when sown. Portions of the samples were 

 thoroughly shaken up with water and the washings examined with the 

 microscope (as is done for certain cereal smuts), but no conidia were found. 

 Further trials were made and the washings centrifuged, but with no positive 

 result. Examination of the mucilage also revealed no conidia. 



Attention was then directed more closely to the external appearance of 

 the seeds composing naturally infected samples. No seeds with lesions or 

 acervuli were found. In the case of one sample a good many seeds were 

 present in which the cuticle of the epidermis of the seed-coat was evidently 

 more or less ruptured. Fifty seeds of this kind were sown in moist sterilized 

 silver sand. In eight days twenty-eight seedlings had been produced ; and 

 no others appeared subsequently. The cotyledons of these seedlings, as they 



