206 Transactions. 



diffidence. As it is well established that the occurrence of silky hairs in 

 great quantity is a xerophytic phenomenon,* it might be suggested that 

 this character in S. saxifragoides is of climatic origin. The Port Hills, upon 

 which S. saxifragoides nourishes, are nowhere higher than 1,800 ft., and 

 most of the seven or eight high points upon them are between 1,500 ft. and 

 1,800 ft. in height ; while the Akaroa peaks are on the average about 800 ft. 

 higher than this, and Mount Herbert just exceeds 3,000 ft. As a conse- 

 quence, the rainfall on Banks Peninsula proper is, and presumably has been 

 for ages, considerably greater than on the Port Hills, the annual rainfall 

 at the Convalescent Home station on the Port Hills being 25-52 in., while 

 that of Akaroa is 44-72 in. There is no geological evidence to show that, 

 since the formation of Lyttelton and Akaroa volcanic areas, Banks Pen- 

 insula proper and the Port Hills have not always stood in the same relation 

 to one another as at present in respect of altitude, rainfall, and climate 

 generally, though when the level of the whole was higher than at present, 

 as it once undoubtedly was, the rainfall upon the Port Hills might have 

 been more greatly reduced, relatively, than that upon Banks Peninsula 

 proper. It might thus be argued that the drier climate of the Port Hills 

 has directly determined the development of S. saxifragoides as above out- 

 lined. If this were the case we should expect to find similar forms 

 developed in other dry localities, but it is doubtful whether any equally 

 suitable situation exists within the limits of distribution of S. lagopus. If 

 the Port Hills form a unique locality in this respect one could understand 

 how S. saxifragoides has such a narrowly restricted range. 



Upon this theory S. saxifragoides and S. lagopus would be classed as 

 two varieties of the same plant, differing only in the degree of efficiency 

 reached, under stress, in the development of their xerophytic apparatus. 



Presumably, also, the other peculiarities of these two plants, such as 

 the woolliness of the rootstock and petiole, might be assigned to the same 

 general cause. Presumably all the six structures above described upon the 

 leaf of S. lagopus, except, perhaps, the marginal glandular structures, would 

 perform a similar function, though attention has here been confined to 

 those two which characterize the upper surface of the blade of the leaf. 



I desire to express my acknowledgements, first, to Dr. L. Cockayne, 

 F.R.S., to whom I owe the original suggestion of this paper, and without 

 whose kindly encouragement and invaluable aid the work could not possibly 

 have been carried out by me ; also to Miss E. M. Herriott, M.A., assistant 

 in the Biological Laboratory, Canterbury University College, who made the 

 microscopical examinations of the various structures and described them 

 (as above) in the most able manner ; and, finally, to Mr. R. Speight, M.Sc, 

 F.G.S., Curator of the Canterbury Museum and Lecturer in Geology at 

 Canterbury University College, who supplied the geological history of Banks 

 Peninsula here given, and also very kindly photographed for me the plants 

 of Senecio lagopus on Mount Sinclair (Plate XIII). 



* E. Warming, Oecology of Plants, pp. 114, 193, 1909. 



