38 THE REV. GEORGE HENSLOW ON THE ORIGIN OF THE 
The angular distance between any two successive leaves, when projected on the same 
horizontal plane, is constant.—The rationale of this law seems inexplicable, because we 
cannot say what causes a leaf to grow out of the axis of a bud at one particular point 
rather than another. All that can perhaps be suggested is, that as an equable distri- 
bution of light may be thus presumably acquired by every leaf, so natural selection may 
have been a determining influence ; but there would seem to be no grounds for assuming 
external influences to have been the sole originating causes *. Whatever be the ultimate 
facts which cause the position of leaves to be what it is, they cannot in the present 
state of our knowledge be determined +. 
This law is found to be true both for normally alternate leaves and for those which 
have arisen on a stem by the development of internodes, on which the lower leaves 
were opposite or whorled in threes. The following observations are the author’s, and 
quoted from the paper alluded to above (р. 654) :— 
“ A change from verticils of threes into 3 was frequent. It takes place in the fol- 
lowing manner :—The first step is to cause the three leaves of the different whorls 
to separate slightly by a development. of their internodes. Then, if any two consecutive 
whorls be examined, the order of succession of the six leaves (No. 1 being the lowest 
leaf) is thus,— i 
6 
1 
in which it will be noticed that the 4th leaf, instead of being over the interval between 
the 1st and 2nd, is over that between the 1st and 3rd; so that the angle between the 
* The * Text-Book of Botany,’ by Sachs (translated by А. W. Bennett), p. 179, may be here consulted. 
t Mr. Hubert Airy has started the proposition that * leaf-arrangement exists for and is determined in the bud." 
And his “ condensation theory " of leaf-arrangement depends upon “ the contact among the balls which [he] uses 
to represent embryo leaves.”  (* Nature,’ vol. vii. p. 442.) 
I venture to eall in question both of these fundamental conditions of his theory. 
That plants generate their buds during a short summer in readiness for the first sufficiently warm weather in 
spring is an obvious fact ; but that they should be obliged to keep the buds so long undeveloped is no fault of theirs, 
but a circumstance dependent upon climate. When once a bud is made, and the only opportunity is the сош- 
paratively short time the plant is in leaf, it matters not whether it remain a week, a month, or six months. The 
duration сап have nothing to do with the formation of it, or of the importance of any peculiar leaf-arrangement. 
If, however, we substitute vernation for leaf-arrangement (as synonymous with phyllotaxis), it will be perfectly 
true; for the half-formed leaves are folded in various ways, so as to to render the bud as compact as possible. 
Moreover there is nothing in the structure of buds to justify the comparison of embryo leaves to balls. They are 
not balls at all, but, rather, conical with more or less flat surfaces. Although the apex of a leaf may first appear аза 
hemisphere, 1 does not retain that form, but elongates into a cone by the time the next leaf emerges from the axis; 
