384} THE NATURAL HISTORY REVIEW. 



By no means can mutual interference be better provided against, 

 and a fairer chance given to all, than by the spiral arrangement. 

 If the number of leaves be very great, the spiral cycles will be very 

 numerous, and the leaves will be smaller, often mere scales, e.^. in 

 the involucre of composites. Other arrangements with the same 

 object are mentioned by Mr. Ruskin,* and these have been curiously 

 overlooked by morphologists, though very worthy of their attention. 



To account for the formation of axillary buds, Mr. Spencer refers 

 to the compound proliferous fronds of Delesseria hypoglossum or 

 Jung ennanniu fur cata, where, if nutrition be abundant, a number of 

 secondary fronds are produced on the primary ones ; tertiary ones 

 sjDring from the secondary ones, and so on. Now, by abbreviating 

 the spaces between these new growths, we shall ultimately arrive 

 at a form like that of a bud. This bud, if nutrition be abundant, 

 will develop itself into a shoot, or if on the other hand the supply of 

 nutriment fall short, a flower is produced, or if it be altogether 

 insufficient, no bud is formed, as in the cases of flowers. But if, 

 from whatever cause, the component parts of the flower receive an 

 abundant supply of nourishment, then those parts become green 

 and leaf-like, and then axillary prolification may arise. 



Mr. Spencer even goes so far as to say that axillary prolification 

 only occurs under such circumstances, a statement which is certainly 

 not correct, in all cases, as the records of Teratology amply show. 

 Mr, Spencer then proceeds to show how the monocotyledonous and 

 dicotyledonous embryos are to be accounted for by his hypothesis. 

 As to the monocotyledons, his explanation is simple. Starting from 

 a proliferous frond, which is rolled up to insure the erect position, it 

 is obvious that the first frond will conceal the second frond, and this 

 in consequence wiU be dependent for a time on the first frond for 

 its support, and must always lag behind the first in its development. 

 This coincides with M. Germain de St. Pierre's account of the ger- 

 mination of Tulipa, wherein the embryo is at first a mere leaf, the 

 plumule being developed subsequently in a spur-like cavity at the 

 base of the first leaf 



But in an exogenous plant, where the erect attitude of the stem 

 is produced by the gradual increase of thickness of the continuous 

 midrib, the second frond will be quite as well, or better placed, as 

 far as regards exposure to light and air, than the first, and so it will 



• Modern Painters, Vol. V. p. 28. 



