Puthybkidge and Laffertv — A Disease of Flax Seedlings. 365 



and each having a minute round pit or perforation of the wall. Frequently 

 there developed from these dark cells new hyaline hyphae, while at times the 

 dark cells reproduced themselves ; and thus an irregular chain of them was 

 formed. With the exception of the terminal cell of each chain which retained 

 its protoplasmic contents, these dark cells appeared to be devoid of contents. 

 (See Plate XX. fig. 2.) 



Although somewhat suggestive of chlamydospores, we are of the opinion 

 that these dark cells are really to be regarded as of the nature of appressoria 

 or organs of attachment similar to those described by Hasselbring 1 for other 

 species of fungi. True appressoria are certainly produced by this fungus, for 

 they have been observed by us on the surface of the stems of diseased flax 

 seedlings raised from seed which, prior to sowing, had purposely been sprayed 

 with water containing conidia of the fungus in suspension. When the seedlings 

 showed the disease on their cotyledons they were watered with a line rose 

 from above, and the newly developed conidia were thus washed from the 

 infected leaves on to the hypocotyledonary stems. The conidia germinated on 

 the stems, each producing a very short and slender germ tube, from which a 

 dark cell with thickened wall and characteristic pit or perforation immediately 

 arose. This cell remained firmly attached to the surface of the stem, and from 

 it there grew out a delicate hypha which penetrated the epidermis of the 

 host. (See Plate XX. fig. 3.) The penetrating hypha was very constricted 

 at the point of passage through the wall of the host cell, but became consider- 

 ably enlarged as soon as the interior of the cell was reached. 



IV. — Pkoof of Pathogenicity. 



In order to find out whether the fungus was capable of producing the 

 disease in healthy flax seedlings the following infection experiment was 

 carried out : — ■ 



Two lots of flax seed, of two hundred each, were sown in pots of soil. A 

 good crop of perfectly healthy seedlings was produced in each case. 



When the cotyledons were fully developed and the succeeding leaves were 

 beginning to appear, the seedlings in one of the pots were sprayed with a 

 suspension of conidia (from a pure culture) in sterile water. The other lot of 

 seedlings was sprayed with sterile water alone. Both pots were then covered 

 with bell-jars and kept in the greenhouse. 



After two days several of the cotyledons of the seedlings sprayed with the 

 conidia-suspension showed rounded, water-soaked areas, whilst no such spots 

 were observable on the control seedlings sprayed with sterile water only. 



1 Hasselbring, H. The Appressoria of the Anthracnoses, Bot. Gazette, vol. xlii., 1906, 

 p. 135. 



