OF SAP IN PLANTS. 7 



bundles which are surrounded and supported by a hard brown 

 layer of cells of a glass-like brittleness. These were not coloured 

 blue ; neither were the vessels in their centre, which evidently 

 contained air, and were to a slight extent unrollable. When 

 this petiole was cut across and the open end dipped in the test 

 fluid, the latter penetrated very rapidly upward into the white 

 air-vessels, driving out the air. If the upper part of the leaf was 

 dipped in the fluid, the phoenomena were the same as in the first 

 case; under such circumstances nothing penetrated into the 

 air-vessels, w^iich consequently are nowhere in communication 

 with the surface (the stomates). 



Aspidium capense. — The phaenomena were exactly the same 

 as in the preceding instance. Here again the stomates on the 

 under side of the leaf conveyed no fluid into the air-vessels in 

 the interior. 



Aspidium filix mas, Sw. — The results did not differ from the 

 foregoing. The brown cells again were not coloured blue here. 

 Hence the Ferns possess distinctly separate paths for the diffu- 

 sion of air and sap. I could not observe any special path for 

 the descending juices, and the existence of such may indeed be 

 doubted, since these plants are supposed to grow only at the 

 points. 



II, Monocotyledons. 



In the preceding section an attempt was made to prove that 

 in the lower cellular plants, in accordance with their homogeneous 

 structure, the fluids passing from the soil into the plants, took 

 no fixed direction, but, soaking through from cell to cell, ad- 

 vanced most rapidly wherever the laxity of the tissue opposed 

 the minimum of resistance. In the Vascular Cryptogams, on 

 the contrary, in the Ferns, it was found that special organs, 

 the streaked vessels, already present themselves, exclusively des- 

 tined to contain gaseous fluids, while the fluids absorbed from 

 the earth first ascended within the looser cellular tissue in the 

 vicinity of those vessels, and were from thence diffused through- 

 out the remainder of the tissues of the vegetable ; not indeed 

 without previously undergoing suitable elaboration and ame- 

 lioration. 



In the Monocotyledonous plants, where the specialization of 

 the anatomical systems becomes more distinctly marked, similar 



