The Effects of Osmotic and Nutritional Variation 297 



abundant energy source, the optimum temperature again dropped 

 to 20 C. Z. eistla did not grow at 30 C on erythritol media. 

 Cytoplasmic membranes being practically impermeable to erytliri- 

 tol, there is no tendency for the concentration of this solute to 

 be equalized inside and outside the cells. The medium outside 

 is in effect diluted until the organism apparently finds it as diffi- 

 cult to obtain nutrients as if an insufficient amount were actually 

 present. Glycerol caused a similar if less striking drop in the 

 temperature at which an absolute growth maximum was recorded. 

 It could enter the cells but, being little or not at all metabolized, 

 could disturb the cellular economy bv its inert presence. Thus 

 any condition which interfered with the chemical energy supply 

 caused not only an absolute reduction in the growth rate, but 

 shifted the whole temperature curve into a lower range. The 

 same general effect was obtained if sub-optimal osmotic values 

 were attempted, as with a fully nutritious sea-water medium 

 witli a value of about 6 Atm. When food was abundant and 

 available, the absolute maximum growth occurred at 25 C; and 

 when the temperature was held at 25 C, the optimum osmotic 

 value was about 17 Atm regardless of the source of the pressure. 

 (This does not include NaCl or erythritol, both of which pre- 

 sented special peculiarities.) 



The ecological implications of temperature-salinity relation- 

 ships in organisms have been considered by several investigators. 

 Kinne (3) discussed the relation between laboratory salinity op- 

 tima and the distribution of polyps in nature. Gold (2), studying 

 the distribution of lignicolous fungi in an estuary, reported tliat 

 more of certain types of molds grow in more saline waters during 

 warmer months, and in fresher waters during cooler months. 

 TeStrake (9) investigating the response of Dictyuchus mono- 

 sporus to changes of salinity and temperature in laboratory cid- 

 ture, found that it would grow at salinities and temperatures at 

 which she could not find it in nature, and suggested that a limited 

 nutrient supply may be responsible for its distribution. Experi- 

 ments with Z. eistla on subsistence media indicate that nutrient 

 quantity alone does not determine the general salinity-tempera- 

 ture relation, but affects it only as an overall shift in the data 

 curves. 



