364 Scientific Proceedings, Royal Dublin Society. 



particularly rich in nutrient material, such as oat-extract-agar. 1 These cells 

 are to some extent suggestive of chlamydospores, but many of them appear 

 to be devoid of contents, and their walls are more irregular in shape and 

 thickness than it is customary to find in chlamydospores. Further reference 

 will be made to them later on in this paper. (See fig. 4, Plate XX.) 



The conidia are developed on and above the surface of the medium in 

 irregular, salmon-coloured masses. They are not, however, so distinctly 

 aggregated together into acervuli as is the case on the living host-plant. 

 Those produced in pure cultures closely resemble those found on the host, 

 and are of about the same size, the average dimensions being 15 - 5/x long 

 by 4;u broad. 



The conidiophorcs are, on the average, usually somewhat longer when 

 developed in pure culture than when produced on the host plant. Their 

 length varies very considerably, the extremes being 16^ and 60^. In breadth 

 they measure. 3ju. They are not aggregated together into clusters or tufts but 

 are scattered irregularly over the surface of the medium. They are usually 

 unbranched, but occasionally they are branched in an irregular manner. 

 Earely, a conidiophore bearing conidia may be produced from a still living 

 cell of a hypha within an adjacent, empty cell, the walls of which therefore 

 form a kind of sheath around the conidiophore and conidia. A case of this 

 kind is illustrated on Plate XX. fig. 6. 



The conidia are produced in succession at the tips of the conidiophores. 

 Their germination can be observed without difficulty in hanging drops or in 

 cover-glass films. A germ-tube is produced as a rule from each end of the 

 conidium, and, after this has occurred, a transverse wall usually arises in the 

 middle of the conidium. 



The setae, in pure cultures, arise from the submerged colourless mycelium. 

 They are similar to those already described, and vary from 150/x to 250/t in 

 length. They are 3/x in breadth, being but slightly thicker than the mycelium 

 from which they spring. (See fig. 5, Plate XX.) 



Development of appressoria. — The following details are based on observa- 

 tions made of the germination and subsequent development of a conidium on 

 a cover-glass film of oat-extract-agar. A germ tube was produced from each 

 end of the conidium, as usual. These germ tubes soon became branched and 

 thus developed into mycelium. At about this time a transverse wall was 

 formed in the original conidium. After two days, terminal, dark-brown 

 thick-walled cells were produced on the mycelium, having irregular outlines, 



1 This contains only the cold water soluble extract of ground Quaker Oats. See Sci. 

 Proc. Roy. Dublin Soc, vol. xiii., no. 36, 1913, p. 578. 



