[Vol. 2 



280 ANNALS OF THE MISSOURI BOTANICAL OAKDEN 



ences are not only biological, such as color formation and 

 changes in the culture media, but also morphological, such as 

 the form of the "Fuszellen" or basal cells of species of Fus- 

 arium, and even gross, as, for instance, differences in form 



of colonies, etc. 



In the first place, artificial culture is of enormous value as 

 it furnishes the proof of the presence or absence of a relation 

 between different forms of fungi. This knowledge not only- 

 gives us a better insight into the development of the organism, 

 but also gives us most important information as to the 

 methods of control. 



In the identification of bacteria cultural methods are abso- 

 lutely necessary as these organisms cannot be determined 

 otherwise. The determination of the host and its enemies is 

 not only desirable on the ground given above, but also because 

 it gives us opportunity for ecological observations. A disease 

 occurs only when conditions are favorable to its development, 

 and these conditions are often pointed out by the composition 

 of the flora of the locality, of which my studies upon the 

 dying-out of alder trees in Germany give you a clear proof. 

 In different localities these trees are killed by a fungus, Valsa 

 oxystoma. The fungus grows into the wood through wounds, 

 especially where branches or twigs are broken off, and kills 

 out parts of the cambium and the bark. The parts into which 

 it does not penetrate remain alive. There was no doubt about 

 the fungus being the cause of the disease, but there were 

 groups of trees which, though the fungus was present, were 

 not quite killed out, the damage done in these localities being 

 much smaller. I hit upon the correct explanation of this con- 

 dition through a study of the special character of the flora 

 under the trees. It was a typical flora of pastures, in which 

 occurred specimens of 7m pseudacorus and retreating areas 

 of Carex paniculata. These two plants are typical inhabitants 

 of the peats, or water borders. It was clear that the locality 

 had been formerly of a peaty character. I could determine 

 that recently the water level had been lowered for the forma- 

 tion of artificial meadows. Without a knowledge of the flora 

 this relation would never have been found, as these meadows 



