8 M. Mohl on the Circulation of the Sap 



somewhat uncertain, or rather it compels us to make a larger 

 series of admeasurements and to draw the mean from them. 



Since, as far as I am aware, no observations have been pub- 

 lished on the velocity of this motion excepting in Chara, the 

 following statements may not be considered out of place. I have 

 only to observe, that all these admeasurements were made at a 

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

 different temperatures exert on the phenomenon has not yet 

 been investigated. In filamentary hairs of Tradescantia virginica 

 the velocity of the current varied from ^-^ to -g^ Par. lin. in a 

 second ; the mean w r as jfo . In the leaves of Vallisneria spiralis 

 the quickest motion was T |-j, the slowest ^q, and the mean 

 T j}j line. In the stinging hairs of Urtica baccifera the quickest 

 motion was -g± J} the slowest ^j T , the mean T j^ line. In the 

 cellular tissue of a stolon of Sagittaria sagittifolia the velocity 

 varied between T ^ and y^y "g> and amounted on the average to 

 F jy ; in the leaf of the same plant it varied between TT Vo an d 

 TJ1)0> ^ ne avera 8>' e being yg-yy line. In the hairs of Cucurbit a 

 Pepo the quickest movement amounted to jfo, the slowest to 

 27W tne avera g e being T yy 7 line. The smallness of these 

 numbers will probably 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 microscope. But it must not be forgotten, that in these ob- 

 servations 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 gra- 

 nules floating in the protoplasma 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 nitrogenous. When granules of chlo- 

 rophylle 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 cur- 

 rent, 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 mediates 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 chlorophyllc granules and the nu- 

 cleus are connected, and which flows in an uninterrupted current 

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

 slight thickness is not very easily seen. Likewise in Chara it is 

 not, as is generally supposed, the cell-sap itself which moves, but 



