EFFECT OF UNILATERAL MONOCHROMATIC LIGHT 

 AND GROUP ORIENTATION ON THE POLARITY 



OF GERMINATING FUCUS SPORES 



Annie May Hurd 



(with two figures) 



* 



Introduction 



The power of light stimuli to produce orientations and tropisms 

 is a phenomenon which has been widely demonstrated in both the 

 plant and animal kingdoms. Not only can unilateral illumination 

 direct movements and growth, but in some species of plants, 

 namely, Equisetum, Fucus, Puccinia, and related forms, natural 

 white light has been found to establish the direction of the first 

 cleavage plane of the germinating spore. Since in such cases the 

 cell on the shaded side of the spore becomes the rhizoidal cell, the 

 polarity of the plant is determined by light, irrespective of gravity. 

 The primary purpose of the present investigation was to determine 

 whether all wave lengths of light, the intensity factor being elimi- 

 nated, are able to bring about this orientation and establish the 

 polarity of the germinating spores of Fucus inflatus. Subsidiary 

 studies which have been made in this connection with interest- 

 ing results are (i) on that most interesting and little known phe- 

 nomenon which I have called "group orientation," consisting in 





the orientation of the cleavage plane and the establishment of the 

 apical and basal ends of the dividing spore by the direction of some 

 other spore or group of spores in close proximity; and (2) on the 

 phototropisms of the young rhizoids in monochromatic lights of 

 equal intensities. v 



In reviewing the literature on biological experiments with 

 monochromatic light, one is struck by the small number of quanti- 

 tative records of the quality and especially of the intensity of the 

 illuminations used. The ordinary light filters used to obtain 

 monochromatic light transmit not only those wave lengths which 

 predominate and give the color to the screen, but also other parts 



25] 



[Botanical Gazette, vol. 70 



