THE VEGETABLE CELL. 95 



— Bot. Zeit. 1843^ ^63) is not dissolved in the plasma, but forms tlie glo- 

 bules, wMch. are destitute of enveloping membrane and of any organization 

 wliatsoever ; the fluid part of the &ap contains no caoutcliouc, and does 

 not coagulate, but dries in the air into a brittle crust, comj^osed of gum, 

 wMch may be re-dissolved in water, whereby the original character of the 

 milk-sap is restored. Therefore the comparison of the milk-sap with the 

 blood, in regard to its organization, is in every respect a mistaken one. 



According to Schultz, the milk-sap exhibits a double motion, an inter- 

 nal one and a circulation. The internal motion, observed both in freshly 

 effused milk-sap and in that still contained in the vessels, depends on the 

 molecules of the sap (by which name the globules appear to be meant), 

 sometimes joining together, and sometimes separating. The same pi'ocess 

 goes on upon the walls of the vessels, and it is most distinctly noticed 

 that the said union and separation takes place, in the same way, between 

 the molecules of the sap and those of the walls of the vessels, as between 

 the molecxdes themselves, and in fact the attraction and repulsion of the 

 portions of the sap take place in a definite direction, so as to communicate 

 a progressive movement to the whole mass of sap. 



It is impossible to make worse observations, and to interpret what is 

 seen more incorrectly, than Schnltz has done in regard to the internal move- 

 ment of the milk-sap. If the globules are small, as is usual, they exhibit 

 the molecular motion of Brown, and, indeed, after having been dried up 

 and re-di&solved in water, just as well as when fresh; if larger, as in the 

 milk-sap of /Samhucus JEhulus, and Musa, there is no molecxilar motion. 

 All the rest is pure fable. 



The flowing movement is, according to Schultz's statements, completely 

 independent of external iafluences, and goes on in the same way in per- 

 fectly uninjured plants as in detached organs and in separate layers cut 

 off the plant, which would prove that it is not caused by mechanical 

 effiision of part of the sap from the walls of the vessels. It is stated that 

 it may often be observed in detached slices, that the sap flows onwards in 

 a wounded vessel into the uninjured part of it, while it flows out from 

 other wounds which lie in the direction of the cuiTcnt. Since therefore 

 the sap flows in one portion of the vessels from the leaves to the root, and 

 in another portion in the reverse direction, a kind of circulation is pror 

 duced (called by Schultz Cyclosis), which, however, does not rim through 

 a definite and perfectly circular path, but parts into numerous circular 

 courses, returning into themselves, in the manifold ramifications and 

 anastomoses of the vessels. 



That the sap must be in motion ixi an injured plant, is self-evident, for 

 it is well known that it flows with force out of wounds in a lacerated 

 milk-vessel : which is caused, not by contraction of the vessel, but by the 

 pressure of the cells surrounding it, since the phenomenon presents itself 

 in plants wherein the canals of the milk-sap do not possess any proper 

 wall. To make out the behaviour of the milk-sap in the vessels, the ex- 

 periments must necessarily be made on uninjured plants. From my own 

 observations, — ^I, like Amici and Treviranus, — ^must deny its movement in 

 the uninjured plant. A leaf of Chdidonium is sufficieiUly transparent 

 when it is laid beneath the microscope with its lower surface upwards^ 

 and covered with a drop of oil and a glass plate, to allow of the appear- 

 ances in the milk-vessels being seen. If we examme in this way a leaf of 



