340 EFFECT OF CHEMICAL AGENTS [Ch. XI 



The following were repellent : — 



alcohol .... 0.1 % potassium sulphate . 1 % 

 ammonium sulphate, 1% sodium malate . 0.5-2% 



It will be observed that all the attracting substances are 

 sugars. 



4. Chemotropism of Hyphae. — While various authors had 

 noticed an apparent movement of hyphee towards certain 

 chemical agents or towards their hosts, the earliest systematic 

 observations upon this subject are those of Woetmann ('87). 

 He placed fly -legs and other nutritive substances in Saprolegnia 

 cultures and noticed that the hyphiB left their original direc- 



FiG. 93. — Negative chemotropism of a hypha of Peziza trif oliorum from the secre- 

 tions of a mycelium of Aspergillus niger. (From Reinhaedt, '92.) 



tions to grow straight towards the food substance. Later 

 Rkinhabdt ('92) showed that hyphee of Peziza may be lured 

 out of their straight direction by spores of Mucor placed near 

 them ; or, again, if a plate of gelatine rich in sugar be placed 

 above a plate of pure gelatine upon which hyphse of Peziza are 

 growing, all hyphae will send up branches to meet the more 

 nutritive surface ; or, again, if Aspergillus niger, whose secre- 

 tions are fatal to Peziza, is placed near the latter, the hyphse 

 cease to grow at a distance of about 2 mm. from the Aspergillus 

 and then send out shoots which grow away from the injurious 

 substance (Fig. 93). 



The most exhaustive studies on this subject are, however, 

 those of MiYOSHi ('94), who worked with germinating spores 

 of Mucor mucedo and M. stolonifer, Phycomyces nitens, Peni- 

 cillium glaucum, Aspergillus niger, and Saprolegnia ferox. 

 Perforated membranes were employed, either in the form of 

 plant epidermis with stomata or of collodion films perforated 



