/. 



PHOTOTROPIST'lS WITT T'ONOCTOOMATIC LIG"T IN FUCUS Alii) VOL V OS. 



The -nower of light stimuli to produce orientations an a 

 /$r"opism3 is a phenomenon which has been widely demonstrated in 

 both the plant ana animal kingdoms. ^ot only canfi unilateral 

 direct movements and r rowth out in some srecies o f r'-jnts, name-* 

 ly ^quisetum, Fucus, 90t- Puccinia_,and related forms, it can 

 establish the direction of the first cleavage plane of the ger- 

 minating snore. Since in such cases the cell on the shaded side 

 of the s^ore becomes the rhizoidal cell. the polarity of the 



plant is determined irrespective of gravit.,- . 



In any attempt to discover t e mechanics of such tropistic 

 reactions,the first problem is to find what wave lengths of 

 light are responsible, and to what extent they are a function 

 of the quality of the stimulus/apart from its quantity or inten- 

 sity. This, then, is the purpose 2$*J^ e c 7 E 3ent ' investigation. 



^f^tL fl^A-jeJLxJl- T% ^fc^t. *>--L#&&i4^tM%*^' ,5^^ SL&brvJL^-'i*) <x*d b ~ 



^&.,,&f>&fi reviewing trie literature ***H&i[Diological experiments 



' >^U- *s~.0.i&-. t^CS^rdf 



with monochromatic light one is struck by fehe abaanoo of quauti 



ave records of -either the quality w tne interisity of the ill- 

 umination. -It ia tfr-woll known f;^ct that "Tae ordinary li^ht 

 filters used to obtain rnonochtomatic lig":t transmit not only 



tho^e vive lengths which predo ; iiu . t.t? i i ive t .e color to the 



screen, but rlso othearts of the spectrum .thariresence of 

 can be detected only by a spectroscopic analysis. Vor example, 

 certain results are frequently ascribed to blue light with no 

 record of just what range of the soectrum was used nor what 

 "ave lengths other than the predominating ones were acting. 



'mother source of inaccuracy has been the neglect or over- 

 sight of the great variation in the intensity or quantity of ra- 

 diant energy transmitted by tjie color screens. Biological 



