332 FORMS OF LEA VES. [March 



phenomenon sufficiently familiar to the cultivator when pruning or 

 " cutting back." The stronger buds exhibited the early or un- 

 specialized condition which the Professor had previously shown to 

 prevail in such Conifera3 as Larix and Ccdrus, — whereas in the genera 

 Sciadopitys and Pliyllocladus in the adult state have no foliage leaves 

 at all, the leaves being all reduced to the form of scales, while green 

 cladodes, which are slender and needle-like in Sciadopitys, and are 

 flat expansions in Phyllocladus, perform the functions of leaves. 

 Tliough Films in the adult state has foliage leaves developed 

 exclusively on abortive spurs, they are scattered on an elongated 

 slioot in the seedling plant ; which condition persists through life in 

 such genera as Abies and Picca. In the seedling Sciadopitys, a few 

 genuine foliage leaves immediately succeed tlie cotyledons, though 

 they entirely disappear in later life. 



The \ Professor considered it scant philosophy to relegate such 

 genera into the relations of children and ancestors, because such a 

 specialized development as had been indicated appeared in the 

 development of this order. 



FORMS OF LEAVES. 



ABSTRACT OF A LECTURE GIVEN AT THE ROYAL INSTITUTION, LONDON, 

 ON 14th FEBRUARY 1885, BY SIR JOHN LUBBOCK, BART., M.P., 

 D.C.L., LL.D., F.R.S., ETC. 



QIE JOHN LUBBOCK said that, greatly as we all appreciated 

 kJ the exquisite loveliness of flowers, it mu.st be admitted 

 tliat the beauty of our woods and fields was even more due to the 

 marvellous grace and infinite variety of foliage. How is this 

 inexhaustible richness of forms to be accounted for ? Does it 

 result from an innate tendency of the leaves in each species to 

 assume some particular shape ? Has it been intentionally designed 

 to delight the eyes of man ? or has it reference to the structui-e 

 and organization, the wants and requirements of the plant itself ? 



Now, if we consider, firstly, the size of the leaf, we shall find 

 that it is regulated mainly with reference to the thickness of the 

 stem, and that when strict proportion is departed from, the differ- 

 ence can generally lie accounted for. This was shown, for instance, 

 by a table giving the leaf area and the diameter of stem of the 

 hornbeam, beech, elm, lime, Spanish chestnut, ash, walnut, and 

 horse chestnut. 



The size once determined, exercises much influence on the form. 

 For instance, in the beech the leaf has an area of about 3 square 



