4 i4 MYCODERMA. 



305. Superficial Vegetations and their Attendant 

 Phenomena. 



All Mycoderma species share the property of forming super- 

 ficial vegetations on the nutrient liquids to which they gain 

 access; beer, wine, beer wort, grape- and fruit-juice, fruit-wine, 

 the residues from the distillation of beer, wine, &c. This circum- 

 stance at once gives rise to the question, Why should this pecu- 

 liarity be general among Mycoderma species, but only shared 

 and in less decided degree by a few races of the morphologically 

 similar wine yeasts ? 



The explanation accepted at one time was that Mycoderma 

 species require oxygen, and therefore form superficial vegeta- 

 tions ; but this theory is imperfect. LINDNER (XXXI.) and WILL 

 (XIII.) are of opinion that the cells of Mycoderma repel water 

 (see p. 392, vol. ii.), and enclose air in their intercellular spaces, or 

 attract air ; and that it is probably this property that enables 

 them to remain so easily on the surface. The researches of 

 MEISSNER (XI.) in this direction show conclusively that air alone 

 is the support of the film vegetations, which are themselves 

 specifically heavier than grape- juice, for instance. This air is 

 firmly retained in the bud aggregations, which often contain 

 many hundred cells, and are extensively branched into brush- 

 shaped masses. In the case of wine yeasts, on the contrary, the 

 bud aggregations, previous to the commencement of fermentation, 

 consist of comparatively few cells. It should also be remembered 

 that, during alcoholic fermentation, in the words of WORT- 

 MANN (XV.), " the small yeast cells are whirled about in a giddy 

 dance, and prematurety torn apart, by the ascending tiny bubbles 

 of carbon dioxide that are soon liberated extensively, with 

 effervescence, by the yeast itself." The bud aggregations of 

 Mycoderma, on the other hand, are able to develop in quiescent 

 liquids hence their larger number of cells. 



When a cell of any species of Mycoderma is sown in grape- 

 juice, beer or wine, it appears from the exhaustive researches of 

 MEISSNEK (XI.) that the phenomena of film-formation proceed in 

 the same way as with many of the film-forming Torulacece. In 

 a very short time the surface of the liquid is found to carry a 

 vegetative growth, formed either by the coalescence of originally 

 separate islands, or by progressive growth from the walls of the 

 vessel. In the first stages of development, the film growth is 

 delicate, flat and very elastic. This dull or partly lustrous surface 

 exhibits a varying number of white spots of different sizes, more 

 or less clearly visible, distributed irregularly or in curved lines, 

 and representing accumulations or cells retaining air between their 

 aggregations of buds. A peculiarity of many species of Myco- 

 derma t to which attention has been drawn by LINDNER (XXXI.) 



