51 



th i :}- responses of the colonies, -..he tira" taken for most 



individuals to ^rosa the dish, i. e. ^' .;a.. , in white li.'ht bO om. 

 from the source in a straight line towards the aro was about 1 

 minute. ?n this distance was doubled, the time was still about 



1 minute. When the c Iture was re::.cved 200 om. many c lonies still 

 requii-ed rrily 1 rainu^e to get icroes Uie dish. 



This effect of Changing the distance was repeated with the 

 No. 70 filter, since as it transmits the longest wav~ lengths the 

 time cf the reaction nhculd be longer. However, they were still 

 too n.^.rt to obviate tho lar.je errors due to the indefinite end 

 points. At a distance cf 25 cm. Lhere was a noticeable collection 

 on tiie li ( shter si 3 of the dish. After 13 minutes nearly all had moved 

 over. At a distance nf 50 cm., ICO cm., :nc 200 cm., the same 

 positive reoulte v/ re c^ 'ith t>ie five minute exposure. Al- 



though failing to si:ow the applicability of the Rosooe-Bunsen L w 

 this exp^riniont r^.cws th<; potency of the long red rays to oause the 

 same pro to tropisms produced by the blue waves when they aot with the 

 right intensity. 



~:ry exposure througiiouc, tli^-^e experiraents was made with a 

 fresh culture BC t.-at in no inst nee was tiiere a ch.ince of the 

 sensitiveness being ..ifior^nt for the succeaaive exposures because 

 of the of -fact I -ceedin t: ; illumination. 



j (^9o3) reports that tiie positive p}:ototropism in 



medium li'jht is reversed by strong light. Att-=>mpts w^ro made t): ere- 

 f re to find the turning point for each screen by .lessening its is- 

 tan*5e fro^i the aro. *t the control behind clear glass was the 



only one in which any negative pho to t ro ;: i 3in could be obtained nnd the 

 response M -re varied at different times. In one experiment, the 



