FUNCTION.] SPIRAL VESSELS. 175 



that spiral vessels perform certain functions, because such 

 functions are proper to bothrenchym in a particular state. 

 It has also been asked, how the opinion that spiral vessels are 

 the sap-vessels is to be reconciled with the fact of their non- 

 existence in multitudes of plants in which the sap circulates 

 freely. To which might have been, or perhaps has been, 

 added the question, why they do not exist in the wood, where 

 a movement of sap chiefly takes place in exogenous trees. 

 And further, it has always been remarked, that, if a transverse 

 section of a Vine, for instance, or any other plant, be put 

 under water, bubbles of air rise through the water from the 

 mouths of the spiral vessels of the medullary sheath. But 

 then, it has been urged, that coloured fluids manifestly rise 

 in the spiral vessels ; a statement which has been admitted 

 when the spiral vessels are wounded at the part plunged in 

 the colouring fluid, but denied in other circumstances. 

 Indeed, to persons acquainted with the difficulty of micro- 

 scopic investigations, the obscurity that practically surrounds 

 a question of this sort must be apparent enough. 



Kiitzing, adopting the views of Schulthess and Oken, has 

 recently asserted that the spiral vessels represent the nervous 

 system of plants ; and that both they and the tubes of pleu- 

 renchym perform the same office in the system of vegetable 

 vitality, as metallic wires in conducting electromagnetical 

 currents. (Linruea, xii. 26. Schulthess, Drei Vorlesungen 

 iiber Electromagmtismus, gehalten in der naturforschenden 

 Gesellschaft zu Zurich : 1835.) 



The use of spiral vessels has been investigated with care by 

 BischofF, who instituted some delicate and ingenious experi- 

 ments, for the purpose of determining the real contents and 

 office of the spiral vessels. It is impossible to find room here 

 for a detailed account of his experiments, for which the reader 

 is referred to his thesis De vera Vasorum Plantarum Spiralium 

 Structura et Functions Commentatio : Bonn, 1829. It must 

 be sufficient to state, that, by accurate chemical tests, by a 

 careful purification of the water employed from all presence 

 of air, and by separating bundles of the spiral vessels of the 

 Gourd (Cucurbita Pepo), and of some other plants from the 

 accompanying cellular substance, he came to the following 



