422 



t^ A R M E RS ' R E GIST ER, 



[No. 7 



ofequal densily ; and so on to the end of the series. 

 At the same time that endosmometiic action 

 commences at the upper end oCthe series, a similar 

 action will commence at the lower end. The 

 lower cellule filled \vili> dense sap and |)laccd in 

 contact with the water contained in the soil, will 

 at once commence attracting that waier to ittelf, 

 and in this way its sap being rendered rarer than 

 that of the cellule above if, will 1)p IransCerred in 

 part to that cellule, and so on to the end of tlie 

 series. Both of these operations, tending as they 

 do to move the sap in the same direciion, will con- 

 spire to produce the same result, viz, the raising 

 of the sjp from the root to the leaves. Again; 

 let us suppose that there is a series of cellules ex- 

 tending liom the surlace to the heart of a tree, 

 each cellule hemg supposed, as in the other case, 

 to be in contact with those next it in the series, 

 and all filled with a liquid of uniform density. By 

 evajioraiion the liquid in the outer cellule of the 

 series is rendered more dense than that of the one 

 next it ; it immediately commences an endosmosis 

 upon that cellule, absiraciing from it a part of its 

 rare fluid and imparling in return a part of its own 

 dense fluid ; this second one op^raies in the same 

 way upon the third, and so on. Such is in fact 

 the condition of the cellules of a plant, and such 

 is one of the ways in which their sap is believed 

 to circulate. It will be perceived that endosmosis 

 accounts for the motion of the sap in every direc- 

 tion, upward, doivn wards, and laterally ; and more- 

 over for tv.'o opposite motions, through the same 

 set of vessels, and at the same time. It also ac- 

 counts for a circulation in cellular plants, and the 

 cellular parts of other plants, such as the pith and 

 medullary rays. In all these respects it agrees 

 with the results of direct observations. Without 

 attempting to determine the extent to which the 

 circulation of the sap is properly attributable to 

 endosmosis, we will dismiss this subject for the 

 present, as we shall have occasion to recur to it 

 again. 



3rd Fiial action. Besides the effects which can 

 be liiirlv ascribed to endosmosis, there are others 

 which we must attribute to motions in the organs of 

 plants caused immediately by the vital principle. 

 It is certain that movements do take place in the 

 organs of plants, which appear to be in no way 

 connected with endosmosis. An instance will be 

 afforded by cutting in two a stalk of lettuce. The 

 milky juice contained in the cellules of the hark 

 will he Ibund to exude li'om the extremities of both 

 portions of the stem. This cannot be caused by 

 a power exerted li'om below, for then the sap 

 would exude fiom the lower portion only ; neither 

 can it be caused by the gravity of ll;e 9t\]), for then 

 it would exude only when the part had its extrenuty 

 turned downwards, whereas in fact, it flows out 

 with equal rapidity, in whatever position the stalk 

 may be placed. This effect can spring from no 

 other cause then from a contraction in the sides of 

 the cellules. Another and a still more striking in- 

 stance, is afForded by the cellules of the leaf of the 

 lettuce during tlie flowering season. Let a leaf be 

 touched ever so slightly, so as not to break the 

 cuticle, the milky juice will nevertheless exude 

 and form a large drop. 



The force witli which the sap is propelled 

 through the stem of a growing plant is much 

 greater than we are generally in the haitit of con- 

 siderino" it. This malliM' has Ikimi tin' sulijec; ol 



some curious and instructive experiments, of which 

 the Ibllowing, from Hales' 'Vegetable Statics,' may 

 be taken as an example. ''April the 6th, at 9 A. 

 M., rain the evening before, I cut off a vine on a 

 southern aspect, at 2 leet 9 inches from the ground; 

 the remaining stem had no lateral branches, it was 

 -} inch in diameter; I fixed on it a mercurial gauge. 

 At 11 A. JVl. the mercury was risen 15 inches 

 higher in the open leg, than in the one attached 

 to the end of the vine, being pushed up by the 

 force of the sap which came out of the stem. At 

 4 P. M. it was sunk on inch. April 7th, at 8 A. 

 M. was risen very little, a fog ; at 11 A. M. 'tis 

 17 inches high, and the [og gone. April 10th. at 

 A. M. mercury 18 inches high ; I then added more 

 mercury so as to raise the surface to a height of 

 23 inches; the sap retreated very little into the 

 sten), upon this additional weight, which shows 

 with what an absolute Ibrce it advances ; at noon 

 it was sunk one inch. April 11th. at 7 A, M. 24J 

 inches high, sunshine ; at 7 P. M. 18 inches high. 

 April 14th. at 7 A. M. 20^ inches high ; at 9"A. 

 M. 22i, fire warm sunshine ; here we see that the 

 warm morning sun gives a fresh vigor to the sap. 

 At 11 A. M. the same day 16i, the great prespi- 

 ration of the stem makes it sink. April 16th. at 6 

 A. M., 19^ inches, rain; at 4 P. M. 13 inches. 

 April 17th, at 11 A.M. 24;^ inches high, rainy 

 and warm ; at 7 P. M. 29^ warm rainy weather, 

 which made the sap rise alfday, there being little 

 perspiration by reason of the rain. April 18th. at 

 7 A. M. 32.\ inches high, and would have risen 

 higher had there been more mercury in the gauge; 

 fi-om this time to May 5th the Ibrce gradually 

 decreased. The greatest height of the mercury 

 being 32^- inches ; the force of the sap was then 

 equai to 36 feet 5^- inches height of water. In 

 another like mercurial gauge (fixed near the bot- 

 tom of a vine which ran 20 feet high), the mer- 

 cury was raised by the Ibrce of the sap 3S inches, 

 equal to 43 ft 3^ in, height of water ; uduch force 

 is about five times as great as that ol' the blood in 

 the great crural artery of a horse, seven times as 

 great as the force of the blood in the like artery of 

 a dog ; and eight times as great as in the same 

 artery of a fallow doe." In the results of the 

 above experiment there can be no error; the mea- 

 surement of a propelling force by means of a mer- 

 curial gauge is one of the most accurate and most 

 unexceptionable methods of measurement which 

 we possess. The force with which the sap was 

 driven upwards, in the last mentioned instance was 

 equal to more than 20 lbs. to the square inch. To 

 recur to the orginal question ; what cause can we 

 assign for so powerful a propulsion of the sap as ia 

 here indicated? Endosmosis will account for it in 

 part ; but it appears to me that we must admit an 

 alternate contraction and dilatation of the cellules 

 themselves as one principal cause. 



Perhaps some nmy object to this explanation on 

 I he ground of the stiffness of the veofetable textures; 

 but let it berecollected that this St iflhess exists, not in 

 I he cellular and vascular tissues, the tissues through 

 which the circulation takes place, but in the woody 

 fibre, which is disposed throughout the plant (br 

 the purpose of givmg strength and consistency to 

 the vegetable structure. The mendirane of which 

 the celluler and vascular tissues are composed, is 

 soft, yielding, and in every way fitted for such al- 

 ternate contracti(tns and dilatations as are sup- 

 posed. 



