282 WENHAM, ON THE CIRCULATION OF THE SAP 



not a symptom of circulation can be discovered : if a leaf 

 suitable for examination be now viewed under an eighth, 

 selecting the more transparent single thickness of cells at 

 the margin of the leaf, it will sometimes be found that the 

 layer of active corpuscules has collected, or run together, 

 on the cell-wall into one, or sometimes two heaps or mounds, 

 being in a torpid and quiescent state. After having care- 

 fully adjusted the object-glass, if the achromatic condenser be 

 focussed on one of these heaps, a bright sky being used for 

 the source of illumination, the slight degree of heat thus ob- 

 tained is sufficient to call into existence the dormant vitality 

 of the active corpuscules. At first, a few atoms on the 

 summit of the mound appear to be loosened, exhibiting their 

 peculiar tremulous motion ; next, a few will start off and take 

 the lead, generally across the cell, the movement of vibration 

 lieing apparently converted into one of direct progression ; 

 immediately, a single file of particles will follow in rapid 

 succession, in a wavering direction from side to side, much 

 resembling a torrent of bubbles arising from a spherule, or 

 small shot, at the bottom of a glass vessel of water, at the 

 commencement of ebullition. Sometimes another line of 

 particles will start off in a different quarter, and, as the heap 

 of corpuscules becomes more fluid and melts down, a very 

 singular commotion takes place ; currents are seen traversing 

 the cell all ways, without apparent rule or order, and two are 

 sometimes seen travelling on the same side of the cell-wall ^w 

 opposite directions : at last, the united numbers and strength of 

 one current will gain the mastery, and determine the ultimate 

 direction of rotation, which will then go on steadily for hours, 

 the chlorophyll granules being duly arranged, and performing 

 their traverse in proper form. 



So far as I have ascertained, heat seems to be the best 

 excitant of the circulatory movement. It is slightly accelerated 

 by the transmission of an electric current ; but this effect may 

 also be due to the creation of a rise of temperature. The leaf 

 of the Anacharis is very sensitive to the application of 

 external reagents ; weak alcohol, ammonia, or acids, instantly 

 destroy the motion of the sap-current. 



There is yet another collection of bodies found in all the 

 various forms of cell composing the leaf of the Anacharis ;'^ 

 they are oblong spicular-looking particles, of a light-brown 

 colour, having an average length of 1-1 1,000th of an inch ; 

 they mostly congregate together in the most vacant part of 

 the cell, either at the centre or one end, and exhibit that brisk 



* Seen also in the Valisneria. 



