RECENT ADVANCES IN SCIENCE 51 



which will enable one to control the reproductive processes 

 of such fungi is thus not only of great physiological interest, 

 but of considerable practical importance in plant pathology. 

 Reference may thus be made in this article to a valuable paper 

 — not of most recent date, but very generally overlooked- — by 

 G. H. Coons on the factors involved in the growth and pycni- 

 dium formation of Plenodomus fuscomaculans (Journ. Agric. 

 Research, v. 713-769, 191 6), in which the relation of growth 

 and reproduction to external conditions is very carefully studied. 

 The fungus in question is one of the Sphaeropsidaceae and is 

 parasitic on the apple. 



It was found that in agreement with the dictum of Klebs 

 there was a wider range of conditions suitable for growth than 

 for reproduction. A small amount of growth will take place 

 in conductivity water (sp. cond. 2 x io -6 ) in vessels of resistance 

 glass. Such a growth is certainly very surprising. The 

 number of spores used for inoculation was not more than fifty, 

 so the growth observed could not be explained by transference 

 of organic material from the spores. The salts required for 

 development under these conditions, and in ordinary distilled 

 water, were no doubt obtained from the glass, but the source 

 of nitrogen, and especially of carbon is obscure ; there is the 

 possibility, first suggested by Elfving, that volatile substances 

 may be absorbed from the laboratory air. It is interesting to 

 note that while in conductivity water there was a just percept- 

 ible growth, in ordinary distilled water the growth was not 

 only better, but a few pycnidia were actually produced. Under 

 the conditions of the experiment conductivity water is the 

 lower limit for growth, but " distilled water " the limit for 

 reproduction. As Coons points out, the sensitiveness to 

 extremely small quantities of salts renders the problem of 

 determining the necessary elements for this fungus almost 

 insoluble with our present technique. 



Up to a certain limit, possibly up to M/50, increase in 

 concentration of the food supply increases reproduction ; after 

 that point increase of food supply retards and finally inhibits 

 reproduction. The organism was found to be sensitive to the 

 reaction of the medium, and the different effect of different 

 media was largely due to the reaction of medium not only at the 

 start, but in later stages of growth. Many media, while having 

 a favourable reaction at start, showed an unfavourable reaction 



