254 Scientific Proceedings, Royal Dublin Society. 



The conidia, which have bluntly pointed ends, are hyaline, single-celled, 

 and of varying shape — oval, cylindrical, and straight forms with a peculiar 

 basal twist are tliose most commonly met with : see fig. 1, Plate X. Stained 

 preparations reveal the fact that the wall of each conidium is slightly 

 thickened at its base, where it was attached to the conidiophore. Their 

 contents are finely granular, and they sometimes possess one or more oil- 

 drops. Though very uniform in breadth, which averages 4/a, they vary 

 greatly in length, the extremes being 9/^ and 20^, with an average of \bfx. 



They are produced by abstriction on the swollen ends of the conidiophores, 

 and occasionally for a short distance along the sides of the latter. Each 

 conidiophore may produce from one to seven conidia at a time ; but three, 

 four, and five are most often seen. When the conidia are ripe they become 

 detached from the conidiophore, and new ones are then produced. Owing to 

 the adherence of the conidia to one another, a little heap or mound of them 

 is formed where the free ends of the conidiophores emerge. 



In the case of the leaf, the conidiophores arise from a loose mass of 

 hyphae situated towards the base of the respiratory cavity beneath a stoma. 

 These hyphae resemble those that permeate the dead tissues of the leaf; 

 but they are not sufficiently numerous or so densely packed as to permit of the 

 aggregation of them formed in the respiratory cavity being regarded as a 

 stroma. The conidiophores continue to grow in the form of an aggregation 

 of rather thick hyaline parallel hyphae towards the stoma, through which 

 their tips eventually emei-ge. As a rule they are simple, but occasionally 

 they are seen to branch in an irregular manner. On emerging, their free 

 ends, which never protrude very far, immediately become slightly swollen, 

 and they begin to produce conidia. Simple unbranched forms were found to 

 measure on an average 21 n long by 6'5;u broad, the latter measurement being 

 made across the broadest part of the swollen apex. 



On flax stems the formation of the conidiophores and conidia resembles in 

 general that on the leaf. In some cases, however, especially when the cortex 

 of the stem is in an advanced stage of disorganization, the parenchymatous 

 tissues beneath the epidermis become ruptured, and the cavities thus formed 

 become filled with a more compact mass of hyaline hyphae from which, here 

 and there, conidiophores arise. These, if they have sufficient space, may 

 produce sub-epidermal conidia as previously described, but more frequently 

 they burst out through a stoma and produce conidia on the surface of the 

 stem. 



As already pointed out, this somewhat compacted mass of hyphae is by 

 no means constantly associated with attacked stems, and even when present 

 it is not sufficiently well developed to merit the description of a stroma. 



