256 DR. J. W. HESLOP HARRISON ON 



colour, and in the other of a glaucous hue due to its secretion 

 of a waxy bloom. Finally, each of these two forms in its turn 

 yields two varieties, one with the leaves glabrous and the other 

 with them more or less hairy. Only one explanation of all 

 these marvellous coincidences appears at all feasible, and that 

 is, that in the derivation of the sections from their hypothetical 

 common ancestor, in the segregation of the section-species 

 into species-types, in the break of the species-type into micro- 

 genes, and in the splitting of the microgenes into varieties, we 

 have a wonderful exposition of evolution on definite lines or, 

 in other words, of orthogenesis. 



As is obvious, no attempt has been made to trace the 

 phylogenetical connection of the various species-types, 

 although that would entail no great labour. One could com- 

 mence with the neutral type of leaflet exemplified by 

 i?. Traae /I i Piwd from it trace by degrees in direct lines every 

 form of leaflet from narrow to broad, from uniserrate to 

 multiserrate, from forms with ronnivent teeth to those with 

 divergent, and so on with every possible combination, just as 

 Eimer followed up the wing patterns in the Lepidoptera. To 

 do so, in the absence of exact evidence as to the true arrange- 

 ment or even the correct starting point, would be unprofitable, 

 for it would simply produce a scheme a fit target for gibes of 

 the same nature as assail the palaeontologist when he arranges 

 his fossil reptilia and amphibia in orthogenetic series. He is 

 always accused of making his arrangement to suit himself, 

 irrespective of the time of appearance on the earth's surface 

 of the creatures with which he deals. My omission cannot 

 aftect in the slightest the genuine orthogenetic course of 

 evolution visible in Rosa, any more than a failure to indicate 

 the order of the figures in the "cat's cradle" would [)rove 

 that they had not been evolved in a definite order. 



Independently of my researches, Almquist, another worker 

 in the same field, travelling by the reverse route to mine, 

 arrived at precisely the same conclusions, but as far as 

 classification is concerned, far ouliii.slanced inc. Cummeiuinsr 



