MONOSACCHARIDES AND THEIR DERIVATIVES 61 



Blastocladiales (94, 123). Less exhaustive studies suggest that the 

 same is true of some species of the Saprolegniales (17, 234). Of sev- 

 eral reports of failure of higher fungi to utilize fructose, that of Shira- 

 kawa (184) is the most convincing, although the fructose was auto- 

 claved in the medium. Several isolates of Streptomyces fail to grow 

 in an agar medium with fructose as carbon source (14). 



Considerable light has recently been thrown on the non-utilization 

 of mannose and fructose through the work of Sistrom and Machlis 

 (185) on Allomyces macrogynus, one of the species of the Blastocladiales 

 previously found not to grow appreciably on these sugars in experi- 

 ments of conventional duration. It is now clear that A. macrogynus 

 can grow on both mannose and fructose with a very long period of 

 incubation; the final growth is comparable to that on glucose. In 

 addition, provision of a small amount of glucose to a medium in 

 which the main carbon source is mannose or fructose allows normal 

 growth with no delay. Both of these observations are consistent 

 with the hypothesis that this fungus — and by implication perhaps 

 others — utilizes fructose and mannose only under conditions which 

 permit or encourage the formation of an "adaptive" or induced en- 

 zyme, although other observations remain to be reconciled with this 

 hypothesis. It would seem, therefore, that utilization of these mono- 

 saccharides is dependent on an enzyme system which is constitutive 

 in some organisms and inducible in others; strains of a given species 

 may fall into different groups in this regard. 



Data from a comprehensive study of 57 fungal species, mostly of the 

 Fungi Imperfecti (116), show that relatively few — about one-fifth of 

 the sample — are completely unable to grow with D-galactose as carbon 

 source in a medium containing asparagine and salts. Many, especially 

 in the genus Fusarium, grow with galactose as well as with glucose. 

 Other fungi, e.g., Helminthosporium sativum, reach the same final 

 dry weight as with glucose but reach it slowly, suggesting that here 

 too an "adaptive" mechanism is at work and that the inclusion of 

 asparagine in the medium may have biased the results by providing a 

 substrate able to support the formation of induced enzymes. Finally, 

 for many fungi galactose is clearly utilized but does not even in a long 

 time period support the same level of growth as does glucose. We 

 may conclude from this and other work that galactose is used by most 

 fungi but is not usually so good a source of carbon as glucose. A sub- 

 stantial number of fungi are unable to utilize it, and it may even be 

 toxic to a few (90, 194). The ability or inability to utilize galactose 

 bears no apparent relation to taxonomic position. 



On comparative grounds, it seems probable that the ability of an 



