ELECTRICITY AND PLAN T-GRO WING. 69 



leads me to say, what you have no doubt already inferred from 

 this discussion, that the injurious effect of the light ceases at 

 certain distances, but that these distances vary for each species of 

 plant. As a rule, there is little injury beyond ten feet, although 

 certain coleus plants standing fifteen and more feet from the lamp 

 are injured. 



This leads me to ask just what these injurious effects are. It is 

 now pretty definitely ascertained that they are due to the highly 

 refrangible or ultra-violet rays of the spectrum ; and these rays 

 are mostl}" absorbed by plain glass. Plants set near the naked 

 light soon show a browning of the leaves and fresh stems, and in 

 some instances the tissues may be killed. But if a pane of glass is 

 interposed before half the plant, the protected portion will be very 

 little if at all injured ; and the projecting leaves will usually show 

 the exact line of demarcation between the screened and unscreened 

 fields. The character of this injury may be learned from the 

 following narrative. On the seventh of last December, a strong 

 heliotrope which had two equal shoots springing from near the 

 base, was placed about three feet from a naked arc of 2,000 

 candle-power. One shoot was screened by a pane of third quality 

 single-thick window glass placed directly in front of it, while the 

 other branch was fully exposed. Neither branch had made fiower 

 buds. The next morning, the light having run six hours during 

 the night, both branches were strongly bent towards the lamp, and 

 the exposed one, as well as the portions of the leaves of the other 

 shoot which projected be^^ond the pane, showed a distinct brown 

 discoloration. After three nights had passed, the exposed foliage 

 Ijegan to curl, but the protected portion was pushing forward very 

 rapidly and had already made good flower buds, while the other 

 showed only the faintest traces of buds. After ten days, the 

 exposed portions were much browned and stunted, and the small 

 flower buds which had been formed appeared to be dead. On the 

 seventh of January, just a month after it was placed before the 

 lamp, the screened branch was in full and normal flower, whilst 

 the other was little more than half as high, most of the leaves had 

 fallen and the remaining ones were small, curled, and dry, and the 

 few almost lifeless flower Inids were unable to open. Other 

 heliotrope plants set six feet from the arc showed trifling injury 

 five or six days thereafter, but the exposed parts flourished and 

 bloomed several- days earlier than branches behind a pane, and the 



