44 ON THE MEDICINAL AND TOXICOLOGICAL 



the specimens -were immersed for inspection ; but none of these 

 afford a satisfactory explanation."* The 0. contexta is an ilhis- 

 tration of the above. 



^, ,, . ^^^ TT 1 ( ^Ii"- Amot s Chroolepus. On 



C/irooiepusArnoUuALook. - ^ 



•^ ( yews. 



" Tliis singular plant," remarks Mr. Arnot, "resembles none 

 other that I know. It is found only on yew trees. The sap of 

 the tree continues to flow through the plant, which also increases 

 in size and thickness, at last becoming a firm, corky, almost hemi- 

 spherical substance, * * * the number of concentric layers 

 marking pretty nearly the number of years the s]5ecimen has 

 been in forming. Tliis, I have no doubt, is caused by the inspis- 

 sation, at the close of each season, of the sap of the tree absorbed 

 by the parasite. I may add that, when well dried, this species 

 takes fire very readily from a spark, and burns like tinder." 

 Arn. in Zitt. ; Crypt. Eng. 



* "Tlie last," he adds, "may be piat to the proof by a very simple contrivance. 

 Let a small portion of the stratum be placed in a ■watch-glass nearly filled with 

 water, and covered witli a circular film of talc, so that its edge may touch the glass; 

 the water will be rendered as fixed as if it was a piece of ice. The glass may now 

 be placed under the microscope, and the oscillation of the filaments viewed without 

 any risk of disturbance from the agitation of the water; by following this course it 

 will be speedily perceived that tlic motion in question is entirely independent of 

 that cause." " The action of liglit as a cause of motion cannot be directly disproved, 

 because we cannot view our specimens in the dark ; but indirectly there is nothing 

 easier. If a watch-glass charged as above be laid aside for a night, it will be found 

 that by next morning not only a considerable radiation lias taken place, but that 

 multitudes of the filaments ha^ve entirely escaped from the stratum; both indicating 

 motion independent of liglit. Rapidity of growth will sliow itself in the prolonga- 

 tion of the filaments, but will not account for tliis oscillation to tlic riglit and left : 

 and still less for their traveling in the course of a frw Iiours to the distance of ten 

 times their own length from the stratum. This last is a kind of motion imexampled, 

 I believe, in the vegetable kingdom. Tliore is anotlier point in the natural history 

 of the Oscillatorice, which favors the opinion tliat they are animalcula?. It is the 

 extremely limited term of their existence, — the communitj-, if I may so call it, lives 

 for several months ; but the individuals die off, and are succeeded by others with a 

 rapidity to which tliere is no parallel among genuine plants. If a small portion of 

 stratum, say one-fourth of an inch in diameter, be left for three or four dajs in a 

 watch-glass filled Avith water, the whole area of the glass will be found covered witli 

 a thin transjiarent pellicle or incipient stratum, derived from the filaments that had 

 successively radiated and (liid in the course of that short period." The O. contexta 

 ■will illustrate the above. 



