848 REPORT— 190B. 



and increasing host is suddenly changed ; familiar leaders &r6 superseded by new- 

 comers who mark their advent by drastic reorganisation. To change the metaphor, 

 we may compare the stages of plant-evolution to the records of changing 

 architectural styles represented in Gothic buildings. The simple Norman arch 

 and massive pier are replaced, with apparent suddenness, by the pointed arch and 

 detached shafts of the thirteenth century ; the latter style, which marked an 

 architectural phase characterised by local variations subordinated to a uniformity 

 in essential features, was replaced hj one in which simplicity was superseded by 

 elaboration, and new elements were added leading to greater complexity and 

 a modification of plan. Similarly the Paleozoic facies of vegetation passes with 

 almost startling suddenness into that which monopolised the world in the 

 Mesozoic era, and was in turn superseded by the more highly elaborated and less 

 homogeneous vegetation of the Cretaceous and Tertiary periods. In taking a super- 

 ficial view of architectural styles we are apt to lose sight of the signs of gradual 

 transition by which one period passes into the next ; so, too, in our retrospect of 

 the changing scenes which mark the progress of plant-evolution, we easily overlook 

 the introduction of new types and the gradual substitution of new for old. The 

 invention of a new principle in the construction of buildings is soon followed by 

 its wide adoption ; uew conceptions become stereotyped, and in a comparatively 

 few years the whole style is altered. As a new and successful type of plant- 

 architecture is produced it rapidly comes into prominence and acts as the most 

 potent factor in changing the facies of a flora. Making due allowances for the 

 imperfection of the Geological record, we cannot escape from the conclusion, 

 which is by no means opposed to our ideas of the operation of the laws governing 

 evolutionary forces, that the state of equilibrium in the vegetable kingdom was 

 rudely shaken during two revolutionary periods. The earlier transitional period 

 occurred when Conifers and Cycads became firmly established, while for the 

 second revolution the introduction of the Angiospermous type was mainly 

 responsible. As in the half-ellaced documents accessible to the student of 

 architecture ' the pedigrees of English Gothic can still be recovered,' so also we 

 are able to trace in the registers imprinted on the rocks the genealogies of existing 

 botanical types. 



In the course of this address I have given but scant attention to the lessons 

 we have learnt and are still to learn as to the family-history of plants. As 

 Professor Coulter says : ' The most difficult as well as the most fascinating 

 problem in connection with any group is its phjdogeny. The data upon which we 

 base opinions concerning phylogeny are never sufficient, but such opinions usually 

 stimulate research and are necessary to progress.' 



We who attempt to read the- records of the rocks may be tempted to magnify 

 the importance of the work, but I do not hesitate to add that botanists as a whole 

 have but half realised the fact that the study of living plants alone supplies but 

 a portion of the evidence bearing on problems of plant-evolution. To ignore the 

 facts that maybe gleaned from the investigation of extinct types is like attempting 

 to draw up a genealogy by merely questioning an individual without consulting 

 the documentary evidence of registers and other chronicles. 



Each successive stage through which the organic world has passed contains some 

 relics of a preceding age ; in comparing the chalk with the calcareous ooze now 

 accumulating on the bed of the Atlantic, Carpenter expressed the partial agreement 

 between the two deposits by saying that we are still living in the Cretaceous 

 period. Dr. Moore's recent researches, demonstrating a striking resemblance 

 between many of the molluscs of Lake Tanganyika and fossils preserved in the 

 sediments of Jurassic seas, led him to describe some constituents of the fauna of 

 this inland lake as so many ' lingering shadows of the past,' while Tanganyika 

 itself is a dwindled remnant of a Mesozoic sea. Similarly our modern vegetation 

 differs enormously from that of the Mesozoic era, yet in the sago-palms of the 

 Tropics and in species of Malayan ferns we recognise proofs of the continuity of 

 plant-types through successive ages. One stage is superseded by another, but 

 some characteristic elements of each period persist into the next, carrying on the 

 traditions of the past and demonstrating the futility of our system of classification 



