On the Use of Air-Vessels in Plants. 87 
fir that has any tap-root, and that, being the deciduous Cyprus, 
and an American tree, could not be known to him. I merely 
mention this, not to detract from these great authors, but as 
lessening the certainty of the evidence when placed in opposition to 
areal law of nature, from which we have as yet seen no variation. 
Before I close this paper, I cannot but mention a circumstance, 
though irrelevant to the subject, which proves, I hope, the accu- 
racy of my observations in this respect, and has given me some 
confidence in them, as agreeing with those of so distinguished a 
philosopher as Mr, Leslie. I observed in one of my letters last 
year, that when I placed the spiral wire suddenly in any degree 
of heat, its motion was all by impulses; whenever I breathed 
upon it, or exposed it to the focus of the solar microscope, its 
Starts were convulsive: now Mr. Leslie in his description of his 
new Atmometer, in which he gives so curious an account of the 
manner in which heat is communicated to water and odours, 
observes, that it is by pulsation. 1 suppose, therefore, that it is 
the heat which eccasions the motion in the delicate muscles of the 
spiral wire, and not any action peculiar to itself. I am, sirs, 
Your obliged servant, 
Cowley Cot, Jan. 14, 1814. AGNES IBBETSON. 
: ——————— 
P.S. In cutting the larger buds I divided the last cover (fig. 5. 
EE): it is the one generally inflated with air, and it now looks 
like a calyx; but it is only a vail to protect it from the water : there 
were three buds, and they were cut in halves, but I could not show 
them. At the inside there was such a confusion I could make 
nothing of it, except that neither pollen nor seeds were yet there. 
The moment the seeds enter, or the pollen gets into the stamen 
(the latter particularly), the parts inflate, and are much larger at 
that time than they ever are afterwards. It is impossible, there- 
fore, not to be sensible of the moment in which it is done, if the 
flower or bud is divided ; for all is in confusion befere, and beauti- 
ful regularity succeeds. 1 shall soon give a view of the buds in 
every different stage, viz. in the roof, in the stem, and just before 
blowing, which will elucidate this subject greatly. But it requires 
such nice instruments of dissection, particularly very sharp and 
pointed scissars, that I am waiting for their formation. I have 
before given the form of the air-vessels in fig. 2. Journal 144, 
‘There are but three sorts, and it is only the shape that differs ; the 
interior parts and the mechanism are the same inall. (Fig. 6) 
are the water vessels in the Menyanthes. This is the sort Mirbel 
dissected, I fancy. He says, ‘Ce ne sont pas des petites utricules 
comme le disent la pluspart des auteurs, mais une membrane qui 
se dédouble, en quelque sorte pour former des vuides contigues 
F4 les 
