190 MICRO-ORGANISMS AND FERMENTATION. 



the species plays a definite part. It forms a white growth (P. 

 album) similar to that of P. candidum occurring in Brie cheese. 

 At a later stage the colour changes to greyish- white or greyish- 

 green. The last two species have large spherical conidia. 



The same genus also includes P. luteum, with a yellow 

 mycelium, changing to green or light brown when covered 

 with conidia. The conidia are small and elliptical, and the 

 sterigmata exceptionally long. This species forms yellowish- 

 brown ascocarps ; the ascospores are provided with prominent 

 transverse stripes. It usually occurs on fruits, causing them 

 to decay, but it may also occur on a variety of other sub- 

 stances. P. italicum seems only to affect lemons and similar 

 exotic fruits, causing their decay. It forms a greenish-blue 

 covering, and has ellipsoidal conidia somewhat larger in size 

 than those of P. luteum. P. olivaceum, occurring on exotic 

 fruits, and less frequently on others, has a distinct greenish- 

 brown colour and large ellipsoidal conidia. 



Most species of Penicillium, and especially P. glaucum, 

 contain a number of different enzymes, one of which, a pro- 

 teolytic enzyme, is present in all species hitherto examined. 

 P. glaucum also possesses a diastase which, according to 

 Laborde, converts starch into dextrin and dextrose. In addi- 

 tion, they contain invertase, maltase, a clotting enzyme, a 

 casein-splitting enzyme, etc., and a poisonous substance which 

 has not been identified. The species occurring in cheese react 

 upon it by the secretion of an enzyme which splits up albumen. 



Species of Citromyces, which have much the same structure 

 as Penicillium, are able under suitable conditions of nutriment, 

 with proper access of air and at the right temperature, to 

 convert sugar into citric acid. The thin- walled conidiophores 

 of these fungi are usually unbranched, sometimes have dilated 

 ends, and possess a terminal tuft of sterigmata. The conidia 

 are very small and spherical. The plants form a greenish 

 covering like that of Penicillium glaucum, and are especially 

 found on acid fruits and fruit juices. 



Two species have been described by Wehmer, C. Pfef- 

 ferianus, forming a velvety coating, and C. glaber with an 

 almost smooth surface ; in other respects they appear to be 

 almost identical. 



