300 
PHYSIOLOGY. 
BOOK II. 
vessels. 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 cir- 
cumstances. Indeed, to persons acquainted with the difficulty 
of microscopic investigations, the obscurity that practically 
surrounds a question of this sort must be apparent enough. 
Klitzing, 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- 
renchyma perform the same office in the system of vegetable 
vitality, as metallic wires in conducting electromagnetical 
currents. (LinncBa^ xii. 26. Schulthess, Drei Vorlesungen 
iiher Electromagnetismus^ gehalten in der naturforschenden Gesell- 
schaft zu Zurich : \8S5.) 
The use of spiral vessels has been investigated with care by 
Bischoff, who instituted some delicate and ingenious ex- 
periments, 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 Functione Comrnentatio : 
Bonnae, 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 conclusions, which, if not 
exactly, are probably substantially, correct : — “ That plants, 
like all other living bodies, require, for the support of their 
vital functions, a free communication with air ; and that it is 
more especially oxygen which, when absorbed by the roots 
from the soil, renders the crude fluid fit for the nourishment 
and support of a plant, just as blood is rendered fit for that 
of animals. But, for this purpose, it is not sufficient that the 
external surface should be surrounded by the atmosphere; 
other aeriferous organs are provided, in the form of spiral 
vessels, w'hich are placed internally, and convey air contain- 
ing an unusual proportion of oxygen, which is obtained through 
