32 



Fig. 51. Spores 

 from the minute 



pustules found on 

 scabby bananas 

 from Cairns, 



Queensland. An 

 infusion culture at 

 the end of twelve 

 hours. 



X 400 



A number of experiments and observations of a similar nature led 

 to the conclusion that the sole organism in the pustules is the fungus 



producing the elongated ellipsoidal spores, 

 and to the conclusion that this fungus is 

 probably the cause of the disease Banana 

 Scab. 



The above-mentioned spores on being 

 subjected to water culture, or rather to 

 growth in water impregnated with the juices 

 of the banana peel, germinated promptly 

 from one or both ends. (Fig. 51 .) After the 

 lapse of twelve hours the mycelial thread 

 from the spore may reach the length of 

 75 micromillimetres. The mycelium at 

 this stage is colourless, for the most part unbranched and without 

 septa, nearly straight, and of about the same diameter as the spore 

 from which it originated. Soon after reaching this size the mycelium 

 begins to branch. Some spores in one of the cultures, spores 

 apparently in other respects identical with those just described, gave 

 rise to conidia by a species of division. (Fig. 53.) In one or two 

 cases the mycelium, after reaching a length of 50 to 75 micro- 

 millimetres, appeared to be forming conidia at the end. 



While it was at most times difficult to discern any trace of mycelium 

 among the cells of a section cut from a pustule, it was always the case 

 that after a few hours mycelium could be seen sprouting from the 

 section in such a manner as to preclude doubt that it originated from 



mycelium hidden away 

 among the mazes of the 

 cellular tissue of the 

 banana. These branches 

 of the mycelium of the 

 disease-producing fungus 

 often grew so vigorously 

 as to pass entirely outside 

 the tissue of the section 

 and thus came into good 

 view. The size of these 

 mycelial threads was such as to lead to the belief that the mycelium, 

 as it occurs normally in the tissues of the banana, is a very attenuated 

 one, often measuring no more than one to two micromillimetres in 

 diameter. A weft composed of mycelium of this calibre hidden away 

 among dark tissues of a varying structure is necessarily difficult to 

 make out, and I think this accounts for the failure to secure what may 

 be regarded as altogether satisfactory data with reference to the 

 internal structure of normal pustules. 



The behaviour of the sections of the perithecium, when allowed to 

 remain in an infusion of banana-peel for twenty-four hours to forty- 

 eight hours, furnished data of a much more satisfactory nature. 



It not infrequently happened that on examining a carefully- 

 prepared section very few spores were found. When this was the 



f. 52. Cross section of a pustule of the banana-scab 

 fungus, a, epidermis of banana ; b, columnar alteration 

 in tissue : c, wall of perithecium ; d, spores borne on 

 basidia. 



