66 Plant-life of the Oxford District 



secondary increase in thickness, but exhibit a marked telescopic growth- 

 effect by the intercalary extension of the internodes of a distichous phyllo- 

 taxis-construction ; the root-system being wholly adventitious from the 

 nodes, and utilizing surface-water. 1 



This short-season type, originally a forest-product, thus becomes the 

 colonizer of open country, or savannah-land, with exaggerated seasonal 

 effect (wet and dry), fruiting with a particularly short vegetative season, and 

 perennating where trees cannot subsist on small supplies of surface-water ; 

 hence passing with equal facility to reduced forms of xerophytic grassland, 

 or to the subaquatic life of the water-logged swamp. On migration to 

 North Temperate regions, smaller and more depauperated types become 

 the familiar vegetation of grassland, enduring winter frost and snow as well 

 as summer drought, vegetating freely over a short period of little more than 

 three months in the year, and utilizing their capacity for telescopic extension 

 for the erection of a short-lived and wind-pollinated inflorescence-system. 

 A closely parallel biological equipment is attained in quite distinct plant- 

 series of the Monocotyledons, as Cyperaceae, Juncaceae, and other families 

 with no direct relation to the Gramineae, to the extent that such forms 

 become characteristic of poor ground, sour water-logged soil, as residual 

 vegetation where little else will grow. 2 



Hence in the migrant flora of a North Temperate country as Great 

 Britain, grass may be taken for granted, as already established, and capable 

 of occupying open land beyond the forest-belt ; that is to say, where the 

 tree-canopy fails, grasses will become dominant, both on dry hill-sides as 

 xerophytic forms enduring extreme desiccation as dry turf, and in swamp- 

 areas as aquatic types mingled with reeds, rushes, and sedges of very similar 

 and convergent biological status. Though there is no direct evidence that 

 open grassland ever existed within the Oxford district, even on the tops of 

 the adjacent hills in post-glacial times, grassland undoubtedly prevailed on 

 the hills of the Chalk at no great distance. Since grasses grow freely where 

 trees will not, any clearing of a woodland area soon results in the production 

 of grassland, which is maintained so long as the woody forms are kept from 

 regenerating. Such grass-tracts by continual cutting, mowing, cleaning, or 

 burning, become the more emphasized, as further progression of the associa- 

 tion is closed, and the conditions for luxuriant grasses are improved ; since 

 all grasses, even the most enduring, flourish best in good well-drained and 

 aerated soil. By close-cutting at the soil-level, the majority of herbaceous 

 perennials may be kept down, and the grass-association is improved by 

 agricultural selection, giving the mantle of green turf characteristic of modern 

 pasture-land and even golf-courses. That is to say, the evolution of pasture 

 is the expression of the influence of human agency on the original tendency 

 to open grassland in the absence of trees, now extended to tracts with 

 better water-supply, fully capable of growing trees, but maintained arti- 

 ficially where trees have been denuded. The pastures become the more 

 artificial as they are mown every year at about the same date, levelled, and 

 the time of cutting adjusted to suit the periodicity of some grasses more 

 than others. 



In allowing for the present condition of pasture-grasses, it must be 

 remembered that a long sequence of equally migrant races of men have 

 colonized the district, bringing with them domesticated cattle as bullocks, 



1 Note that the erected monaxial Zea Mais, familiar as a ' typical Monocotyledon ', is a wholly 

 secondary expression derived by agricultural selection as a mutant of Euchlaena mexicana, the 

 multiaxial form of which is cultivated as Teosinte. 



For account of the organization of Forest Bamboos, cf. Troup (1921), Silviculture of Indian 

 Trees, p. 990 ; Brandis (1911), Indian Trees, p. 660. 



* Schimper(i9o3), Plant-Geography, Eng. Trans., p. 591, General Oecology of Grassland. 



