PHYSIOLOGICAL EFFECTS UPON CULTURE MEDIA. 21 



the time needed for other observat ions upon these cultures about 15 

 days. Where liquefaction occurs during the active growth of the 

 colony it definitely indicates the secretion of ectoenzyms capable of 

 tins digestion. Long-deferred liquefaction may result from such 

 secretion or from the liberation of endoenzyms by the disorganizat ion 

 of mycelium. 



Color production. Certain species cause marked changes in color 

 in some of the substrata in which they grow. Such reactions are 

 usually produced upon certain media and qoI on others. They are 

 therefore selective reactions. For example, one species produces a 

 bright yellow color in media containing milk sugar, such as milk or 

 peptone-milk sugar-gelatin; but no color in plain potato agar. Some 

 <>\' these colors are soluble in alcohol to form brightly colored solu- 

 tions. The chemical nature of these substances has not been studied. 

 but the reactions themselves have been thoroughly tested for a few 

 species. In these species color production uniformly follows the 

 proper culture condit ions. 



Production of fluid upon surfaci of colony. — The presence upon the 

 surface of the colony of Large drops of transpiration water which may 

 be colorless or brightly colored by excreted products is common. 

 Although a transient character dependent to some measure upon 

 the humidity of the air in the culture vessel for its prominence, there 

 i^ much difference between species in this particular. 



Technical descriptions of these fungi have always been based. 

 theoretically, upon morphology only. In such descriptions the 

 host or substratum has been more or less definitely indicated. Where 

 the organisms are parasites or saprophytes closely restricted to par- 

 ticular substrata and conditions, this practice can perhaps be justly 

 supported. With omnivorous cosmopolitan saprophytes cultural 

 study quickly shows morphology to be affected greatly by changed 

 conditions or altered composition of media. Further, very many 

 of these orga.ni.sms have no known special habitat. A description 

 based upon a specimen of one of these species found in the held, 

 without comparative culture, might possibly contain some peculiar 

 character which would identify a specimen of the same species when 

 next found, but this is only a possibility. In practice the descrip- 

 tions we have are nearly useless. 



The introduction of cultural study carries with it the necessity of 

 recognizing at least the most striking physiological data. With 

 these species of PeniciUium such data have been found as reliable as 

 morphology. Further, the careful definition of morphology and 

 reactions upon specified substrata under known conditions is only 

 amplifying and rendering definite the two items habitat and local- 

 ity- which have always been included in plant descriptions. In 

 recent years the students of ecology and of experimental evolution 



