244 



BOTANICAL GAZETTE 



[SEPTEMBER 



determining photo-presentation as the light intensity or the duration of light 



exposure. 



Guttenburg 5 has also worked on the question of whether it is the direc- 

 tion of the ray or the relative intensity of the light on the two flanks of the 

 plant organ that determines the phototropic orientation. His evidence points 

 to the former as the determining factor. It is doubtful, however, whether 

 his methods are to be compared in reliability with those of Mast, 6 which 

 seem to prove the intensity theory. 



Schanz 7 has just published a striking article on the effect of light of dif- 

 ferent ray lengths on the development of plants. This is one of the very rare 

 articles that makes a really large contribution to the subject. This is assum- 

 ing, of course, that his results and conclusions will be confirmed by later work. 

 The plants were grown in beds covered with glass of various kinds that cut 

 out different regions of the spectrum. The nine beds received the following 



■ 



light: (I) without cover, ray lengths X 300 /ul/x and longer; (II) covered with 

 ordinary window glass, ray lengths A. 320 /x/u, and longer; (III) euphos (a) glass 

 only, ray lengths A. 380 fxfx and longer; (IV) euphos (b) glass only, ray lengths 

 A. 420 /xfx and longer; (V) red glass only, ray lengths X 560 tt/x and longer. By 

 combining yellow, green, and blue violet glass with euphos glass he got yellow, 

 green, and blue violet lights respectively that were free from most of the 

 ultra violet rays. He numbered the yellow VI, the green VII, and the blue 

 violet VIII. 



Cucumbers grown in these beds showed a rather rapid increase in rate of 

 growth and vigor as one passed from bed I to bed V; that is, as more and 

 more of the ultra violet and other short rays were removed. From bed V 

 to VIII the rate of growth and vigor fell off. The curve representing the 

 growth rate in the various beds was a mathematical curve with the peak at V. 

 Petunia, Fuchsia, Chrysanthemum, Lobelia, Begonia, and Oxalis esculenta 

 showed similar curves. In fact, practically all of the plants studied showed 

 similar behavior in the rising part of the curve (beds I to V), but several 

 showed irregularities in the falling part of the curve (beds VI to VIII). The 

 potato was weakest in yellow, stronger in green, and still stronger in blue 

 violet. In green lettuce the leaves became continuously longer and more 

 slender as one passed from beds I to V. They w r ere very slender in red, and 

 there was a misproportion between midrib and flat portion of the leaf. In 

 yellow the disturbance was still greater and the plants showed poor chlorophyll 

 development. In green these plants showed similar but less marked dis- 



*Gu 



fro, H. V.j Untersuchungen uber den Phototropismus der Pflanzen 



II. Xeue Versuche zur Frage nach der Art der Lichtperception. Ber. Bot. Gesells. 

 37:304-31°- 1919- 



6 Bot. Gaz. 51:304-305. 1911. 



7 Schanz, Fritz, Wirkungen des Lichts verschiedener Wellenlange auf die 

 Pflanzen. Ber. Bot. Gesells. 37:430-442. 1919. 



