Macfarlane, The Sensitive Movemeuts of some Flowering Planta. 



183 



ments likewise prove this. In the case of sensitive plants each 

 species is not affectecl alike by the same intensity of the more 

 refrangible rays. Thns if we attempt a rough approximation by 

 noting temperature, Oxalis stricto, and other species are visibly 

 affectecl at 20° C; Cassia Tora at 24° C, C. nictitans at 26° C, 

 Oxalis dendroides at 28 ° C and Mimo&a pudica at 30° C. The 

 various relations thus indicated by temperature hold also ior light 

 intensity. This being so for flowering plants, a much greater 

 ränge of action may be expected amongst Fungi and allied 

 groups. The above facts then indicate that the more refrangible 

 rays promote active chemical change, and that above a certain 

 Optimum of intensity they are decidedly destructive. 



If we attempt now to answer the second question as to why 

 the blue-violet rays are injurious, we are met by diftieulties that 

 are due chiefiy to want of Information. The information however 

 may soon be forthcoming. Ward's Suggestion ior Bacillus 

 anthracis is that „it appears at least possible that the baetericidal 

 action of the light is due to its destructive influence, in presence 

 of oxygen, on the fatty matters or other oxidisable substances 

 forming the reserve materials of the spores." And later he says : 

 r Of course it may turn out that the action of the light is more 

 profound than the simple explanation offered assumes, and that 

 the physiological properties of the protoplasm are deepl) r con- 

 cerned. u 



If we apply these theoretical considerations to sensitive plants 

 we are met by the fact that the visible results of the intense blue- 

 violet rays are the same as for other kinds of Stimuli, whether 

 mechanical, thermal, chemical, or electrical. I have already ex- 

 pressed the view*) that such movements may be more readily 

 explained by chemico-physical activity of the protoplasm itself. 

 But it should be stated that in every leguminous sensitive plant yet 

 examined by the writer each contractile cell of the primary pul- 

 vinus tissue, or as in Cassia Tora, each epidermal cell of the 

 leaflet pulvinus, contains a clear refractive sphere that has a definite 

 position in relation to light. This body gives all the reactions of 

 an oil, and usually has traces of tannin. During and after its 

 Solution the cell nucleus is revealed within, surrounded by small 

 granules that had been imbedded in the oily matrix. We get some 

 idea from this of the extreme complexity of the chemico-physical 

 mechanism, but at present our knowledge is not sufficient to permit 

 of any explanation of the presence of the oil. 



These observations emphasize the view already expressed by 

 several investigators that orange, yellow, and green screens to the 

 protoplasm, wliether in the form of pigmented walls, of pigmented 

 cell sap, or of chlorophyll are of a protective character, and permit 

 the normal functions to be carried on unimpeded by the action of 

 the more intense blue-violet rays. But while such pigments are 



*) Biological Leetures. 



