TRANSACTIONS OB' SECTION D. 627 



ever, affect the outer scales, which remain as before without any increase of size. 

 But as the leaves have increased in size and the buds have not,' the leaves can no 

 longer retain their original arrangement in the bud. If. for instance, we compare 

 the buds of the oak and of the beech we see tliat while the leaf of the oak is 

 longer than that of the beech, the bud of the oak is, on the contrary, shorter than 

 that of the beech. 



Under these circumstances what must happen ? The leaf grows and becomes 

 longer than the bud ; it is therefore necessarily bent into a curve. Jiut an 

 entire leaf, if thus thrown into a curve, would necessarily fall into folds, the 

 number being determined by the number of ribs or veins. For such folds, however, 

 there would be no room within the narrow limits of a bud, or rather perhaps they 

 would be inconvenient because they would leave more or less empty spaces. 



This may be rendered more clear by taking a piece of cloth or paper, folding it 

 up, and then throwing it into a curve. It will then necessarily fall into one or 

 more folds. If it were strengthened, as an oak leaf is, by three or four side-ribs, 

 there would be a fold between each two ribs. As a matter of fact, however, from 

 the absence of space the membrane where the fold would be is not actually 

 developed. We may imitate this by removing them. If this be done the result 

 will be the formation of sinuses, rounded at the base, closely resembling those so 

 characteristic of the oak leaf. These sinuses are due then, as I believe, to the 

 curvature of the leaf, owing to the shortness of the bud in comparison with the 

 length of the leaf. 



The young leaf is not only curved, it is wrapped round the interior leaves. 

 The result of this is that one side of the leaf is folded within the other ; the one 

 therefore being on the outside has more space than the other. The two sides of 

 the leaf are in fact differently situated, and this I believe accounts for the second 

 point — namely, the want of symmetry. 



The oblong form is an advantage from the way the leaves diverge from the 

 stalk. 



In this manner the interesting peculiarities of the oak leaf may be accounted 

 for. 



The paper was illustrated by diagrams, specimens, and models, and the proba- 

 bility of the cause suggested being the true one was enforced by the application of 

 a similar argument, which clearly explains the peculiar form assumed by the very 

 interesting and curious leaves of the tulip-tree. 



7. On the Leaves of the Quelder Rose. By Sir John Lubbock, Bart., F.B.8. 



On the Modifications of Electric Organs in Elasmohranch Fishes. 

 By Professor J. Cossae Ewart, M.D. 



9. Observations on the Migration of Fishes. By Prof. J. Cossar Ewart, M.D. 



SATURDAY, SEPTEMBER 14. 

 The Section did not meet. 



