— 
RESISTANCE OF TUBES TO COLLAPSE. 215 
self sufficiently studied ; in order to explain which it will be necessary to 
point out that around the bulb of this plant, will be found from one to four 
bulblets, which at the time the plants begin to dry are easily separable from 
the parent : it therefore happened that upon pulling up the stem, the bulblets 
became detached and caused a thicker plant to spring up where I had 
thought it destroyed. This shows how even the pulling of a plant of this 
character is inefficacious for its destruction ; and it may further be appealed 
to as one of those accidental experiments which almost every plot presents, 
for it may be observed that in these plots many facts (of agricultural interest 
especially) are daily unfolded by the College Garden experiments, that I 
have not commented upon in this report. 
As regards the Carduus acaulis, it will here only be necessary to say that 
having found a new locality in Wilts. for Carduus twberosus, I have brought 
a few specimens into my garden, and as will be seen from a separate paper 
which I have laid before the Section on this discovery, I have an idea that 
the C. tuberosus is but a hybrid. I am cultivating the C. acaulis and C. 
acanthoides side by side, in the hope of being able to prove this by experi- 
ment. 
8. FLowERING AND ORNAMENTAL PLANTs.—These for the most part 
consist of such specimens as may be of use for teaching, or ornament in the 
lecture-room ; and many of them afford interesting examples of departure 
from recognized typical forms as to be of value in teaching, whilst others 
seem to grow wildly and lose their whole cultivative characters. As yet I 
have not attended to the cultivation of flowers merely as illustrations of trans- 
mutation of species; but Iam convinced that such genera as Primula, Viola, 
Myposotis, and Malva, &c., would furnish a vast amount of interesting matter 
as the result of time and attention bestowed on their investigation. 
Here then, for this meeting, must end my notes; if, however, the Section 
‘should deem them, or the class of experiment they have reference to, worthy 
of continuation, the subject offers a field sufficiently wide, and, I think, 
‘important for much future investigation and description, as it appears to me 
that it is upon the noting and collecting such facts as can only be obtained 
where the subjects of them are under constant observation, that we can hope 
for much light being thrown upon the at present obscure subject of specific 
_ distinctions ; and here, whilst experiments are being made upon this matter, 
_ itis not too much to state that other facts of great interest are constantly 
presenting themselves, so that while we are collecting evidence of a scientific 
kind we may also expect to make experiments tending to useful practical and 
economic discovery. 
On the Resistance of Tubes to Collapse. 
By Wiuu1aM FarrBairn, F.R.S. 
_ Ar the joint request of the British Association and the Royal Society, a 
series of experiments was undertaken to determine the laws which govern 
_ the resisting powers of cylindrical tubes exposed to a uniform external 
pressure, and from them to determine their strength, and deduce rules for 
_ proportioning the internal flues of boilers and similar vessels. 
_ Hitherto it has been considered as an axiom of boiler-engineering, that a 
cylindrical tube placed in the position of a boiler flue, was equally strong in 
_ every part when subjected to a uniform external pressure, the length not 
of 
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