96 ANATOMY AND PHYSIOLOGY OF 



an uninjured plant growing in its pot, or even a detached leaf burnt at 

 tlie cut surface of the petiole, to prevent effusion of the milk-sap, the sap, 

 which at first is disturbed hy the motion of the leaf and the pressure to 

 wliicli it is exposed in spreading li out upon the stage of the microscope; 

 quickly comes into a state of re^t ; then, if the petiole is cut off with a 

 pair of scib&ors, a most rapid current immediately commences, which goes 

 on till the clFu^ed sap coagidates and prevents iiiore from being poured 

 out. If the same experiment is ]nade on tlie leaves of Tragopogon, in 

 which the milk-vesselh run in tolerably parallel direction, a conviction 

 may soon be obtamcd, by cutting oif first the tip and on another the 

 base of the leaf, that the sap always flows in t]ie direction of the wound. 

 When the sap is at rest in a leaf, the slighest pi^cssure upon the leaf suf- 

 fices to produce a most rapid flowing for a few seconds, and when the 

 pressure is i^emoved, it flows back in the opposite direction. Amici shewed 

 that when, by an oblique position of the muTor of the microscope, the 

 sunlight was thrown upon a paxi) of the leaf on one side of the field of 

 vision, the sap was set in motion, and the current was reversed when the 

 light was tlu'own u2)on the opposite side. These experiments place it 

 beyond doubt to me, that the Gijdosis has no existence, and that the move- 

 mant of the sap is produced by mechanical causes. The fmiiher proof of 

 Gyclosis found by Sohultz in the currents of the protoplasm contained in 

 the cells, which lie asiiumes to be the same milk-sap, contained ia ramifi- 

 cations of the milk-vessels penetrating the cell walls, needs no word of 

 refutation. 



Schultz derives from the pretended organization and movement of the 

 milk-sap, the conclusion that the latter plays the same part m plants as 

 the blood does in animals* He therefore calls it vital-sap Qehenssajl) 

 latex I have shewn that the bases of his arguments are hicorrect obser- 

 vatioDs; but, independent!}'' of that, the milk-sap is wholly unfitted on 

 other accounts to serve as an universal nutrient juice. In the first place, 

 it only occurs in a comparatively small number of plants, and, in fact, 

 without a definite relation to the rest of their organization and systematic 

 position. Schultz, indeed, asserts the contrary, suice he declares that he 

 has found the milk-vessels in the majority of the families investigated by 

 him ; but his anatomical researches are altogether tmworthy of trust, for 

 he mingles together the most different tilings. In the second place, the 

 composition of the milk-sap is quite unsuitable in the stated purpose. 

 Schultz compares the caoutchouc coagulum with the fibrine of the blood. 

 The comparison is, as shewn above, incorrect, because the caoutchouc is 

 not dissolved in the fluid of the milk-sap ; but leaving that out of the 

 question, the comi^osition and chemical properties of caoutchouc are such, 

 that no constituent of x)lants could be named less fitted for the peculiar 

 nutrient substance, for there does not exist an indication of a possibility 

 that it is capable of metamorphosis within the plant. Thirdly, the com- 

 position of the milk-sap varies exceedingly in different plants, and fre- 

 quently in closely-allied sj)ecies, although most milk-saps agree in being 

 poisonous. Side by side with the acrid milk- sap of BuphoThia canarien- 

 sis stands the AUd juice of E. halsamifera ; beside the narcotic juice of 

 Palaver J the acrid juice of Chdidonium; beside the narcotic of Lactuca 

 Q)vrosa^ <fec., the innocuous juice of other species of Lactuca ^ beside the 

 frightfully poisonous juice of Antiaris toodcariaf the harmless juice of 



