liAFFEiiTY — Disease of CulttDated I^lax. 255 



The swollen ends of the conidiophores have been very carefully examined 

 for the presence of sterigmata, but these have never been seen. Occasionally 

 very minute local thickenings have been found in the walls at the ends of old 

 empty conidiophores, which may, perhaps, represent points at which conidia 

 were produced, but no general thickening of the wall of the conidiophore has 

 been observed. 



III. — Isolation of the Fungus and Beiiavious in Pure Cultures^ 



Owing to the abundance of conidia produced by the fungus, there is no 

 difficulty in obtaining it in pure culture. Such cultures, starting in each ease 

 from a single conidium, have been derived from the fungus present on 

 diseased fruits, seeds, leaves, and stems, as well as on the affected tissues of 

 plants exhibiting the " stem-break " phase of the disease. In every case 

 detailed studies proved that the organism obtained was the same. It is 

 easily cultivated and grows reasonably well on a variety of nutrient media. 



Diluted conidia-suspensions in wort gelatine, or beef-extract gelatine, 

 were plated out in Petri dishes in the usual way. When the gelatine had 

 solidified, the dishes were examined with the low power of a microscope, and 

 the positions of isolated conidia were marked. When germination had 

 commenced, a single germinating conidium, together with a small piece of the 

 medium surrounding it, was transferred, witli aseptic precautions, to each of 

 several tubes of slanted media ; hence the growth in each tube was the pro- 

 duct of a single conidium. 



Por purposes of comparison, the fungus isolated from different parts of the 

 host and from flax plants growing in widely different localities in Ireland lias 

 been grown on the following media: — beef-extract gelatine, beef-extract 

 agar, extract of Quaker-oat agar, ground Quaker-oat agar, cooked green flax 

 stems and nutrient agar made from the watery extract of cooked green flax 

 stems ; but irrespective of its source of origin, the fungus behaved similarly 

 on the various media used, and showed no morphological or cultural differen- 

 tiation into strains or races. 



The fungus develops its mycelium comparatively slowly and sparsely on 

 all the media tried, but conidia are always produced in great abundance. On 

 ieef-extract gelatine and agar growth is poor, the mycelium being, for the most 

 part, submerged. It is hyaline, septate, and branched, the individual cells 

 being thin-walled and irregular in size and shape, and frequently much 

 swollen. The surface of the medium becomes covered with a cream-coloured 

 mass of conidia resembling a bacterial growth. The conidia are somewhat 

 larger on the gelatine medium than they are on the host, their dimensions 

 averaging 15|U x 5/j. On agar they averaged 14/.( x 4'6^. Many of them 



