Professor A. C. Seward — Floras of the Past, 563 



may be safely laid under contribution as aids to broad generalisations. 

 Detailed descriptions and the enumeration of small collections are 

 a necessity, but there is danger of the student neglecting the 

 application of his results to problems of far-reaching import. 



There is no more fascinating task than to follow the onward 

 march of the plant- world from one stage to another and to watch the 

 fortunes of the advancing army. We see from time to time 

 war-worn veterans dropping from the ranks and note the constant 

 addition of recruits, some of whom march but a short distance and 

 fall by the way; while others, better equipped, rise to a position of 

 importance. 



At long intervals the formation is altered and the constitution of 

 the advancing and increasing host is suddenly changed; familiar 

 leaders are superseded by newcomers, who mark their advent by 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 was replaced by one in which simplicity was superseded by 

 elaboration, and new elements were added leading to greater 

 complexity and a modification of plan. Similarly, the Palaeozoic 

 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 in turn superseded by the more highly elaborated and less 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 superficial 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; new 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-effaced 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. 



