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XIX. On the Use of Air-Vessels in Plants, By Mrs. 
IBBETSON. 
Sins,— Siz George Staunton observes, “that the leaf of the 
Nymphea Nelumbo, besides its common use, has from its peculiar 
structure, growing entirely round the stalk, the advantage of de- 
fending the flewers and fruit within its centre from any contact 
with the water, from-whatever depth, (unless in case of a sudden 
inundation,) until it attains the surface.” But this property is 
common to all water plants. There are curious facts appertaining 
to plants of this kind, well worth showing, since they are phzno- 
mena which serve as general rules in nature ; and to attain and 
collect these, has, from the first of my dissecting plants, been my 
most ardent desire ; especially as (in this case) they are never, 
or very rare/y varied from. The fact which I now wish to prove, 
is the use which Nature makes of air-vessels in plants, while I 
attempt also to explain how air in general is received and placed 
in them. It was the universal opinion of all the physiologists of 
the last age, that all plants have air-vessels : but dissection has 
convinced me that ¢his is a mistake ; that when found, they are 
too large and beautiful not to be seen and acknowledged: but 
they are to be discovered in water- and semi-water plants alone. 
There is indeed a quantity of air mixed in the vessels % all ve- 
getables, and from this circumstance arises that process which 
accelerates or retards the flow of the sap ang other juices: the 
mixture of air in the sap-vesseJs is the source of the most won- 
derful part of the formation of plants in general, since to that is 
owing the constant fluctuation which the heat er cold produces 
in the several vessels, filling and emptying them as the thermo- 
meter rises or falls: thus, when the cool of the evening, or even 
a cold blast approaches, the air which nearly fills half the sap- 
vessels is condensed into a much smaller compass ; this calles 
a momentary vacuum, which opens the innumerable leaf-valves 
of the plant, and in succession those of the hairs, and admits a 
stréam of rain er dew into the sap-vessels, which then being per- 
fectly replenished, the returning sun as quickly converts into 
oxygen for the restoration of that purity of air so necessary to 
health; and carbonic acid gas, for the formation of the bark 
juices, and other combinations. This process takes place in 
‘some measure, in water- as well as in dand-plants: but with 
respect to real air-vessels, vessels filled with air alone; they ap- 
pear, from all the dissections or study I have made on them, to 
*be placed in the plants merely to support them in the water ; 
_ and to be fixed in different directions according to the attitude 
a “* on the stream in close contact with it, then the leaf-stem 
in which the vegetables are required to stand. When the leaf is 
Vol, 43, No, 190. Fel. 1814. — F increases 
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