206 Scientific Proceedings, Royal Dublin Society. 



Germination of the Conidia. — In hanging drops of rain-water ripe conidia 

 germinate within a few hours. The individual cells of the conidium first 

 become swollen, and it thus becomes somewhat constricted in the regions of 

 the septa. Germ tubes may arise from any or all of the cells of a conidium. 

 No fragmentation of the conidia into their constituent cells with a subse- 

 quent rounding off, previous to germination, as described by Smith 1 for 

 Fusisporum Solani Mart., has been observed by us in F. cceruleum. Germinating 

 conidia are shown in fig. 3. Plate VII. 



Isolating the Fungus, — In no group of fungi is it more essential than in 

 the genus Fusarium that the starting-point of a pure culture should be a 

 single conidium, and we used this method. There is no particular difficulty 

 in the matter in this case, seeing that the spores are large; and isolated 

 individuals can, with comparative ease, be found and kept under observation 

 under the microscope, on poured plates of suitably diluted conidia-suspen- 

 sions. Thence transference singly to media in tubes is not a matter of real 

 difficulty to a skilled worker. Appel and Wollenweber found the isolation 

 of this species difficult, but that is probably because the material from which 

 they started was a more or less heterogeneous mixture of the various kinds 

 of organisms found associated together on rotten potatoes, and was not, as in 

 our case, a pustule produced on the surface of a tuber in the comparatively 

 early stages of a definite dry-rot. 



If diseased material in not too advanced a stage of decay is available, it 

 is also a comparatively easy matter to obtain cultures by removing, under 

 aseptic conditions, small portions of tissue from the junction between the 

 still healthy and the diseased portions of the tuber, and placing them on 

 suitable nutrient media. Many of such cultures, if prepared with skill, will 

 be found to be pure ; others will become contaminated with stray germs 

 during preparation. Failing diseased material in just the right condition it 

 can be prepared by first inoculating a previously externally-disinfected, 

 healthy tuber from a conidial pustule, and, when the rot has proceeded 

 sufficiently far, by removing small portions of tissue, as described, to suitable 

 media. For critical work, of course, this method is not admissible. Never- 

 theless, we have found that in the case of F. cmrvleum, at any rate, a 

 considerable proportion of the cultures thus obtained are pure. 



Growth in Pure Cultures. — The fungus has been cultivated on more than 

 a dozen different media, but they have not all proved equally suitable. 2 The 



1 Smith, Worthington G. Diseases of Farm and Garden Crops. London. 1884. p. 31. 



" It should be stated that in none of our cultures have any forms of fructification 

 other than conidia or chlamydospores been developed, although we have been successful 

 in obtaining the development of perithecia in vitro with pure cultures of Hypomyces 

 Solani, Nectria Rubi, and with one or two other fungi. 



