THE DESCENDING SAP 



141 



it was almost dark, the whole 

 plant seemed to glow with a sort of 

 pulsing phosphorescence." 



The Common Nasturtium was 

 also luminous in a less degree, the 

 luminosity in this case extending to 

 the leaves, which, it is further stated, 

 gave off " a blue vapour of extreme 

 tenuity." " I put a leaf of Nasturtium 

 on the stage of a microscope," con- 

 tinues the canon, "and, having 

 focussed it for the central spot from 

 which the nerves branch off, under an 

 inch and a half objective, I brought 

 it into a room nearly dark. Looking 

 at it then through the microscope, 

 I found that the leaf could be dis- 

 tinctly seen almost by its own light. 

 The appearance of the luminous 

 vapour floating over its surface (like 

 moonlight over rippling water) was 

 strikingly beautiful. The whole leaf 

 seemed to twinkle with points of 

 light the main ribs radiating from 

 the common centre shining out like 

 a silver star. These effects are best 

 witnessed after a day of hot sun- 

 shine." . 



Canon Russell's discovery of phos- 

 phorescence in the leaves of Tropce- 

 olum introduces a new feature into the inquiry, and is of much interest. 

 Moreover, the fact that the luminosity remained in or on a leaf which had 

 been detached from the plant and removed to quite a different spot, and 

 that it was visible alike in daylight, dusk, and lamplight, might be held to 

 dispose once and for ever of the optical illusion theory ; for how could such 

 a theory be sustained in view of the persistence of the phenomenon ? And 

 yet it is strange that so few have beheld this manifestation. 



So far the references have all been to orange-coloured flowers ; and it 

 will be remembered that Coleridge wrote : 



Tis said at Summer's evening hour, 

 Flashes the golden- coloured iiower, 

 A fair electric flame. 



The False Dittany (Dictamnus fraxinella} of which there are several 

 garden varieties, white, red, and purple may be said to occupy an unique 



FIG. 177. FALSE DITTANY (Dictamnus 



fraxinella). 



From glands on the flower-stalk this plant exudes an 

 etheric oil which is volatilized in warm weather, and if 

 a light is applied beneath the flower the vapour takes 

 Many modern experimenters, however, have failed 

 to get such a demonstration. 



fire. 



