452 



THE MONILI^ AND OLDIA. 



Oidium lactis, Fresenius, a fungus widely distributed in Nature 

 and in the fermentation industries, is generally known as milk 

 mould, being almost invariably found on sour milk, and also on 

 the surface of unclean dairy utensils, cheese, &c. It is of such 

 regular occurrence in butter that LASER (II.) proposed to utilise 

 this circumstance as a biological test for that substance. Other 

 common habitats of the fungus are the surface of packages con- 

 taining pressed yeast, on pickled gherkins, commercial starch, 



green malt, and in breweries, where 

 it occurs on the sludge-filter bags, 

 wooden utensils, and storage casks 

 (as a white efflorescence), also in 

 waste waters, the dung of domestic 

 animals, &c. 



When viewed by the unassisted 

 eye, the fungus has the appearance 

 of a delicate, white down composed 

 of fine threads, though sometimes it 

 is mealy and dry rarely yellow and 

 mucinous whereas in artificial cul- 

 tures on various nutrient media it 

 always forms a uniform snow-white, 

 closely matted, furry covering. The 

 appearance is exactly the same on 

 nutrient liquids, so that an Oidium 

 culture can always be identified at 

 the first glance. Old cultures exhibit 

 isolated upstanding masses of hyphse, 

 resembling Basidiomycetes. LINDNER 

 (XL.) described similar forms, owing 



FIG. 2o6.-0idimn lactis. their ori g in to the fact of the film 



2V, hypha with a number of lateral plectenchyma in giant cultures being 

 branches; F, a branched thread perfectly gas- tight, and consequently 

 in course of septation ,- vi, dis- forced upward, like bubbles, by the 

 55X^1S carbon dioxide liberated during for- 

 Magu. 600. (After Lindner.) mentation, and being prevented from 

 escaping at the sides owing to the 

 colonies adhering firmly to the nutrient medium at the margin. 



The mycelium in the fungoid mass, which is often extensive, 

 consists of septated and very irregularly branched hyphae, the 

 members of which are comparatively long (Fig. 206). In young 

 mycelia, especially during the germination of the conidia, the 

 cells are tubular, septation only occurring later ; and the conidia 

 are difficult to distinguish from the short cylindrical cells. The 

 conidia, which have the typical Oidium form, are developed most 

 completely when one of the hyphse raises itself above the level of 

 the substratum and divides into short cells by septation, when 

 growth at the apex is concluded. The various cells soon become 



