662 



LIGHT AND LIFE 



en 

 en 



2.00 

 1.80 

 1.60 



T 1 1 



• SINGLE DETN. 



o 2-3 DETNS. 



e 4-5 DETNS. 



H 6 OR MORE DETNS 



> 



o 1.40 



^ 1.20 - 



3 1.00 



o 



0.80 



^ 0.60 



a: 



0.40 



0.20 



340 360 



420 440 



LENGTH 



460 

 IN 



480 500 520 540 



380 400 



WAVE LtNb I h IIN m>j 



Fig. 9. .Action .spectrum for the positive cur\aturc of Pliycoinyces sporangio- 

 pliorcs, obtained by the balance method, using blue light as reference. (From Curry 

 and Gruen, 19,')9). 



There is another similarity with Avena. Phycomyces shows a 

 second type of phototropism in the shorter-wavelength region of 

 the ultraviolet. The curve of Fig. 9 falls towards zero at about 310 

 m^u,. Beyond this point the plants show negative curvature. Fig. 10 

 reproduces a series of pictures of a group of Phycomyces sporangio- 

 phores which are being illuminated from the right with ultraviolet. 

 Curvature begins rapidly; by about 35 minutes some of the sporangio- 

 phores overshoot the 90° and thus become exposed on their opposite 

 flank and, as a result, show reversed curvature. The rate of curving 

 is evidently very high. 



A preliminary action spectrum for the negative curvatures in the 

 ultraviolet has been published (Curry and Gruen, 1959), but it is 

 not sufficiently detailed to draw conclusions as to the photoreceptor. 

 There is a general similarity to the curve for Avena in the same region. 



