20 



" Leaf Variation in Trailing Plants." 

 Dr. W. Ainslie Hollis, F.R.C.P. 



Read December 8th 1886. 



The object of the paper, as stated by the author in the com- 

 mencement was twofold. First to call attention to the variability 

 of leaves in individual plants, and secondly to show the adapta- 

 tion of peculiar varieties of leaf-form to the circumstances of 

 individual life, and to the advantages of the plant thence accruing. 



Among the more interesting and noticeable examples of varia- 

 tion of leaf-form might be mentioned those seen on the passion- 

 flower. On a branch exhibited were ovoid, tripartite and 

 quinquefoliate leaves. On a bramble were shown a ternate 

 leaf in the lower part followed by simple ovate leaves in the 

 upper. In a specimen of woodbine, simple leaves were found at 

 both extremities and compound leaves in the centre. In the 

 common woodbine the leaves may be seen in every stage of 

 transition from the simple oval, to the serrated leaves of 

 complex forms. The simple leaf is probably the more stable 

 form. The various species of Rubus also present an extraordinary 

 variation of form on almost every plant. Not only in the 

 Passifiora, but in all cases according to Lubbock the palmate has 

 been developed from the cordate form. The leaf of the black 

 Bryony shows a great tendency to variation from the general 

 type, and may be taken in illustration of Lubbock's theory. The 

 ivy affords remarkable examples of leaf-variation from those of 

 simple outline to the most deeply lobed. 



The author thought that this redundance of form was rather 

 due to an excess of formative power, " than," as Grant Allen puts 

 it "a failure of growth between the principal ribs." The 

 development of the leaves' of Tropreolum majus were then noticed 

 in which a palmate leaf is changed into an orbicular one, and 

 experiments described which the author made to ascertain the 

 ratio of growth of different parts. 



In the second part of his paper, " the adaptation of leaf- 

 variation to the exigencies of individual plant life," Dr. Hollis 

 laid most stress on mimicry, as generally giving the plant some 



