Notes and Comments. 85 



direction of light in effecting phototropic responses in foliage 

 leaves. In accordance with the teachings of physics we may 

 assume that it is only the light absorbed by the photo-sensitive 

 elements of a stimulable plant organ that is capable of settmg 

 up a phototropic stimulus. The hght rays penetrate the 

 tissues unequally but symmetrically. The extent to which 

 this takes place can be shown by means of a simple piece of 

 apparatus which may be called a Phytentoscope. By keeping 

 the photo-sensitive region of a foliage leaf in a fixed position 

 it can be shown that the orientation to light is determined by 

 the varying extent to which the rays of hght penetrate the 

 photo-sensitive elements. The photo-sensitive elements of a 

 foliage leaf probably consist of parenchymatous cells in the 

 apical region of the leaf-stalk. Experimental evidence is 

 brought forward to show that it is probably mainly in the 

 cortex that the stimulus is received and transmitted. There is 

 no evidence to show that the epidermis and pith take any 

 large part in the process. 



PHYSICO-CHEMICAL ACTIVITIES. 



If the phototropic response is due to the physico-chemical 

 changes set up by the Hght absorbed, then it follows that — 

 (i) The intensity of the physico-chemical changes depends 

 upon the amount of light absorbed. 



(2) The extent to which the light is absorbed depends 

 upon {a) the degree of penetration of the light, and [b) 

 upon the selective absorption of the photo-sensitive 

 elements. 



(3) The degree of penetration depends upon {a) the intensity 

 of the hght that impinges upon the stimulated region, 

 and (b) upon the angle or angles at which the incident 

 rays strike it. 



We see, therefore, that the distribution of the physico- 

 chemical activities in the photo-sensitive tissues is dependent 

 upon both intensity and direction of Hght, and since the 

 direction of movement may be determined as the resultant 

 of the varying physico-chemical activities in the whole of the 

 sensitive region, we must conclude that both intensity and 

 direction of light are necessary factors in the phototropic 

 response. 



SPORE COLORATION IN THE AGARICACE^. 



Dr. Wager read a second paper entitled ' Spore-Coloration 

 in the Agaricaceae.' He stated that the use of spore-coloration 

 as a basis for the classification of the Agaricaceae is artificial 

 and imperfect. There is no clear line of demarcation between 

 the various colours, and the designation of the colours in the 

 text -books is very indefinite and unsatisfactory. A beginning, 

 has, however, been made by members of the Mycological 



1918 Mar. 1. 



