INFLUEXCE OF LIOHT oX KL'MVCETES. 59 



Ward >m)j)urt.s this view \t\ the peiKOiial observation that the 

 colourless spores of Oiiliuiii lurfin, Clialara iiiyoMlenna, and SfW' 

 channnijceK pyrijumtix were killed by insolation, whereas this 

 was not the case with those of AKjmyillu/' ifhttirw, J'fiii»'illiuiii 

 rnigfuituhi {!'. i/ltiitrum), Mucor ract'inoKux, ami Uutrijtin chitiiu. 

 It must not, however, be forgotten that the greater j)ower of 

 resistance oiTered by tliese spores may well be tlue to the con- 

 siderable tiiicUness of the meml)rane. Nevertheless, as tho 

 foregoing discoveries by Eifving have shown, all means of pro- 

 tection fail in presence of prolonged insolation. 



With regard to the influence of the Roentgen rays on the 



vitality of tho Eumyeeto, an expei iiiHiit was idiiducted on 



Phycomyceti niferijt by L. Eiiuaha (I.), but furnished no definite 

 results. Further research on this point is therefore desinible. 



^ 233. Chemotropism General Remarks on the 

 Enzymes of Eumycetes. 



Chemotaxis has already been explained (>; 41 of vol. i.)as the 

 attraction or repulsion of motile microorganisms by chemical 

 stimulants. Motile cells, which are therefore capaVile of being 

 similarly inlluenced, are al.so found among the Kuinycetei!, 

 namely, the zoospores (J5 220) of the Oouiycefef! And Clit/triiliacea; 

 i.e. fungi that do not come within the scope of the present work. 

 In the case of the other higher Kunniciti.K, the elVects of such 

 a stimulus are manifested by the atTected individual either 

 develoi)ing with particular strength towards the seat of the 

 stimulus (inclining thereto) or turning in the oi)posite direction. 

 These phenomena are termed respectively positive and negative 

 chemotropism. The earliest statements and ob.servation.s on 

 this point were made l)y W. Pkkkkkii (IV.), then by J. WuUT- 

 MAXX(Vlll.), y\. Wauu(V1.). M. (K KEixnAKUT(I.). and others. 

 More thorough investigations were conducted by ^1. Mivosni 

 (I.) with Miiror muodo, J'fiyrdiiiyri's jtiten.<, liJiizopua m'/jricaiif, 

 l\'nirilliu)u ijlauriDn, and A.<j"'riiillii.i iiiifr, in various ways; 

 inti'f alia, by sowing tlie spt)res of these fungi on the surface of a 

 finely perfomted mica plate, the lower side of which was in 

 contact with the .solution of the substmce under test. The 

 ft)llowing were found to act as powerful stimulants? on the.se 

 fungi: ammonium phosphate, among the inorganic substixnces ; 

 and asparagin, dcxtiin, and various sugars (.sjiccharose and 

 glucose) among organic compounds. (Il\cerin proved almost 

 entirely inactive. 



The minimum ipiantity of any stimulant capaV)le of pnxlucing 

 a chemotactic or chemotropic elYect on fungi had already been 

 termed the marginal limit (Srhtnlhum-rth = litenilly, " threshold 

 value") bv W. rtelVer. This value was a-scorti«ined bv MiVosui 



