FUNCTION.] RATE OP MOVEMENT. 335 



different temperatures exert on the phenomenon has not yet 

 been investigated. In filamentary hairs of Tradescantia vir- 

 ginica the velocity of the current varied from -ji^- to -pfe Par. 

 lin. in a second ; the mean was T ig-. In the leaves of Val- 

 lisneria spiralis the quickest motion was -p^, the slowest -^-o, 

 and the mean -ply line. In the stinging hairs of Urtica bac- 

 cifera the quickest motion was -^-ly, the slowest -^fy, the 

 mean yi^- line. In the cellular tissue of a stolon of Sagittaria 

 sagittifolia the velocity varied between y-^-g- and l \ 6 , and 

 amounted on the average to -^yq- ; in the leaf of the same 

 plant it varied between Vo ai *d TUTTO* the average being 

 -raV-r nne - I n the hairs of Cucurbita Pepo the quickest 

 movement amounted to yy-o, the slowest to 8 7 I 6 , the average 

 being -j-yVr li ne ' The smallness of these numbers will pro- 

 bably surprise many, especially when they are compared with 

 the apparently considerable velocity which the circulation of 

 the sap, in Vallisneria for instance, exhibits under the micro- 

 scope. But it must not be forgotten, that in these observa- 

 tions the motion is seen quickened several hundred times. 

 The above admeasurements were made in the following 

 manner : while I observed the passage of the image of the 

 globule across the field of a glass micrometer fixed in the 

 ocular, I counted the strokes of a second-pendulum. What 

 the nature of the granules floating in the protoplasm may 

 be, cannot in most cases be ascertained on account of their 

 minute size ; but it appears that they are in all cases coloured 

 yellow by iodine, and are, therefore, most probably nitro- 

 genous. When granules of chlorophyll occur in the cells, 

 they are situated either, as for instance is the case in the 

 hairs of the Melon, isolated and close to the walls of the cells 

 without having any definite relation to the current, and only 

 a few move on with the current, or they are all connected 

 with the current and move with it, as in Stratiotes aloides 

 and Sagittaria sagittifolia. This form effects the transition 

 to Vallisneria, in whose cells it is not the cellular sap itself 

 which is in rotation, as appears at first sight, but a mucila- 

 ginous fluid with which the chlorophyll granules and the 

 nucleus are connected, and which flows in an uninterrupted 

 current along the cell-walls, but on account of its great 



