46 Plant-life of the Oxford District 



This implies that the Pre-glacial period may have been quite 10 times as 

 distant, or may be estimated in terms of a million. Yet, according to 

 C. Reid, no less than 75 species^ of the present flora were even then sufficiently 

 established to be fully recognizable ; leaving the period required for their 

 full establishment indefinitely remote. All these plants, again, had come 

 to this country as migrants, specifically fixed and long-established ; the 

 place as well as the time of their origin is left open. Allowing a margin of 

 error for such determinations, it begins to be evident that species, as they 

 are now reckoned, must go back at least to the Tertiary. If genera became 

 broken into modern specific forms in the Tertiary, for which a time-distance 

 of something like 50-100 millions has been claimed, Families of still older 

 order may date back to the Cretaceous ; as in turn the primary lines of 

 divergence between Gymnosperms and Angiosperms may be of Palaeozoic 

 antiquity (some 300-400 millions). The fact that forest timber-trees 

 (Cordaitineae) were in existence in the Upper-Devonian, indicates the 

 immensity of the gap still required to account for the rise of a timber-tree, 

 producing flowers and seeds, from the algal prototypes of the transmigra- 

 tion, 2 and the possibly hundreds of millions of years required to build the 

 organization of the arboreal habit from its constituent factors. 



V. THE HAND OF MAN 



Of all influences which have been brought to bear on the character of 

 the flora up to the present time, that of human agency is overwhelmingly 

 preponderant, and the more disturbing as it is often erratic in action and 

 bearing consequences wholly unforeseen. Little objection can be taken to 

 such influences by the naturalist, however much he may pine for a virgin 

 forest at his door, since it is only by such human interference that the locality 

 has been made available for human life in the first instance, and to it we owe 

 the fact that we are here at all to examine what is left of the original 

 condition. 



Without going back to the remote ages when the mammoth came down 

 to drink at the river-terraces, 3 or the reindeer and woolly rhinoceros wandered 

 over the site of the city, it is clear that even at the beginning of the historical 

 epoch the land was covered with dense forest, in which roamed wolves, wild 

 boar, and red-deer; the forest-canopy being only broken on the exposed 

 more arid slopes of some of the adjacent hills, and again in broad stretches 

 of swampy ground formed by the damming up of the river in winter flood- 

 time with its narrow outlet below Sandford. 4 In every type of floristic region 

 the effect of human effort and interference is to be traced; not only as 

 considerably modifying the nature of the ecological associations, but rendering 

 them largely of temporary duration, liable to disturbance the effect of which 

 is wholly incalculable at any time. Thus of the original Forest-land no trace 

 remains in anything which may be regarded as approaching its primary 

 condition. With clearings for arable and pasture-land extending over the 

 slopes of the river-basins above the alluvial line, patches of woodland remain 

 as Wytham Wood and Bagley Wood, each of an area extending to about 

 a square mile. Smaller portions survive as copses (Radley Wood, Stow Wood, 



1 C. Reid (1899), Origin of British Flora, p. 171. 



2 Thalassiophyta and the Subaerial Transmigration, Bot. Mem. iii, 1920. 



3 Bones of Elephas primigenius were dug up in the gravel of Magdalen College Grove iu 1921. 

 Traces of woodland extend practically to the top of Shotover ; a few trees (Pine and Elm) 



grow on the exposed top of Cumnor Hurst. Forest-land deteriorated to Willow and Alder-scrub 

 may come down to the alluvium near the present river (Godstow Holt). Only Wytham Great 

 Wood, and more definitely Nuneham Woods, still come down to the river-margin. 



