334 MOHL'S ACCOUNT OP EOTATIOK. [BOOK n. 



some and the origin of others at fresh places where none pre- 

 viously existed, this phenomenon has been already described 

 by others, especially by Meyen and Schleiden. 



" The following phenomena, which I observed on the sting- 

 ing hairs of Urtica baccifera, yield, together with this change 

 of position of the sap, current, and nucleus, a further proof 

 against the existence of a vascular system or inner cells. I 

 left a leaf of this plant lying for a couple of days on the table, 

 so that, with the exception of the large ribs and the stinging 

 hairs situated on it, it was perfectly dry. Now in these faded 

 hairs the currents appeared to be very much altered ; some 

 still existed in the natural state and were in motion, but in 

 the greater portion the granules had separated, and were dis- 

 tributed with tolerable uniformity over the surface of the 

 cellular membrane, and exhibited a molecular motion. When 

 some of the hairs which had been cut off had lain in water 

 for half an hour and were again full of sap, the granules 

 arranged themselves more and more into filaments, between 

 which were some free spaces and in which the circulating 

 motion was completely restored. In this case, therefore, 

 every possibility of the currents being inclosed between mem- 

 branes is excluded; indeed the form of the currents of sap, 

 as exhibited in the stinging hairs of this plant, is opposed to 

 that view. The movement of the current is mostly very 

 irregular; if we leave Chara out of the question, it is most 

 regular in Vallisneria, but even here it is far from being 

 uniform. The sap flows quicker in one cell than in another, 

 in one current quicker than in the adjacent ; frequently stop- 

 pages occur at some spots, so that the sap becomes increased 

 for a time, and some granules are overtaken by those behind 

 them, &c. This inequality of the motion renders the deter- 

 mination of the velocity of the current somewhat uncertain, 

 or rather it compels us to make a larger series of admeasure- 

 ments and to draw the mean from them. Since, as far as I 

 am aware, no observations have been published on the velo- 

 city of this motion excepting in Chara, the following state- 

 ments may not be considered out of place : I have only to 

 observe, that all these admeasurements were made at a tem- 

 perature of 66 to 68 Fahr., and that the influence which 



