HABIT, STRUCTURE, AND APPEARANCE. 15 



substances have been found to affect the growth of cultures more 

 slowly. Most species grow normally in extremely dilute solution-. 

 hut continue to irrow w ell or even richly until the solutions reach con- 

 cent rat ions of considerable osmotic pressure. 



Temperature. The species studied are mostlj saprophytes of wide 

 distribution. They are therefore able to thrive within a consider- 

 able range of temperature. Comparatively few of the species tested 

 grew normally at blood heat (37° C). At this maximum many of 

 them either failed to grow or were actually killed. Within the range 

 of IJ to :!o ('. the rapidity of development in mosl species, as 

 indicated by the production of colored fruit, increased with the rise 

 in temperature. The lower temperatures affect the rate of fruit for- 

 mation without, as a rule, preventing such development. Cultures 

 held at 10° to 20° (\ reached a development fully equal to those held 

 at higher temperature, only in longer periods. 



HABIT, STRUCTURE, AND APPEARANCE OP COLONIES. 



Many series of comparative cultures indicate that any colony of a 

 particular species will reproduce the same characters whenever 

 grown upon a particular medium under particular conditions. The 

 differences between many species of Paticilliuiu are so striking to the 

 eye as to enable one familiar with t hem to identify the several species 

 immediately. These same differences are, however, so difficult to 

 define, and in many cases so transitory, as to render their expression 

 in form to insure recognition very difficult. Recognition of specie- 

 depends at best upon a series of observations of these characters 

 throughout one, and usually more than one, generation upon two or 

 nioie substrata. A discussion of these characters follows: 



Fruiting period. — In comparing cultures of related forms it is 

 found that the time necessary for development from the spore to the 

 production of ripe conidia differs for the different species, but that 

 periods in the different species bear a comparatively constant rela- 

 tion to each other when all are grown under the same conditions. 

 Similarly the length of the growing and fruiting period varies in the 

 several species. In some species the mycelium produces new coni- 

 diophores and masses of conidia among or overgrowing the old for a 

 considerable length of time. In some a secondary growth of white 

 or even colored hyphae often overgrows the fruiting area. In others 

 the chains of conidia once started continue to increase in length for 

 several weeks, until the conidia! fructification becomes a mass 1 mm. 

 or even more in length. In still others but a single crop of conidia 

 is developed and t he mycelium apparently dies or is totally exhausted 



ill ;i few days. In some species the center of the colony unit II res and 



dies while the margin continues to grow and produce new conidio- 



phores for some time. The habit of the species in the production of 



