CHAP. II. 
ELEMENTARY ORGANS. 
301 
the root, by their own vital force, from the earth and water. 
In a hundred parts of this air twenty-seven to thirty parts are 
of oxygen, which is in part lost during the day by the surface 
of plants under the direct influence of the solar rays.” 
With such evidence of the aeriferous functions of the spiral 
vessels, it will doubtless to many appear probable that this 
question is settled, as far as spiral vessels, properly so called, 
are concerned. Whether or not ducts have a different function 
is uncertain ; it is probable, however, from the extreme thin- 
ness of their sides, that they are really filled with fluid when 
full grown, whatever may have been the case when they were 
first generated. 
Link, who formerly considered trachenchyma a part of 
the aeriferous system, now declares its function to be that 
of conveying nutritious secretions. [Element, ed. 2. i. 188.) 
He considers his nelv opinion proved by certain plants, which 
he had grown in a solution of prussiate of potash, having had 
their spiral vessels stained blue when afterwards grown in 
sulphate of iron. (See Appendix.) 
Gaudichaud has also been appealed to, as being of the same 
opinion ; but this botanist seems to have ascertained nothing 
more than that articulated bothrenchyma conveys fluid, 
which is a very different thing. {^eeAnn. des Sc.) 
It requires no argument to prove that the office of cinen- 
' CHYMA is to convey the elaborated sap of a plant to the places 
where it is needed, and especially down the inner parts of 
‘ the bark of ^ygens. For all details concerning this matter, 
we must wait for the appearance of Professor Schultz’s memoir. 
In regard to the functions of air-cells and lacunce^ it may be 
sufficient to remark, that in all cases in which they form a 
part of the vital system, as in water plants, they are cavities 
regularly built up of cellular tissue, and uniform in figure in 
-the same species; while, on the other hand, where they are 
not essential to vitality, as in the pith of the Walnut, the Rice- 
paper plant, the stems of Umbelliferae, and the like, they are 
ragged, irregular distentions of the tissue. In the former case 
they are intended to enable plants to float in water; in the 
■latter, they are caused by the growth of one part more rapidly 
vthan another. 
