10 



Plant-life of the Oxford District 



tract on which the Botanic Garden was planted (1633). This land had been 

 taken over by St. John's Hospital, which was later reconstructed as Magdalen 

 College (1458). The area was still liable to total submergence by exceptional 

 floods, until the ' New Cut ' was formed after the last record rise of 1882 (as 

 marked on the present bridge), and the level of much of the garden has been 

 raised above the flood-line ; though the Cherwell still occasionally tops the 

 garden wall when in full flood (5 ft. above summer level). The present 

 Departmental buildings have arisen as accretions based on greenhouses of 

 different epochs. 1 



The nature of the environment, to which the plant-life of the district is 

 subjected, may be conveniently considered from the standpoint of: 



(1) Climatic Factors, including sunlight, temperature, rainfall, etc., 

 as meteorological conditions, and 



(2) Edaphic Factors of soil and substratum, as essentially geological 

 in their primary relations, including the drainage system of the rainfall 

 in the form of springs and river-systems. 



Climate. 



Meteorological records for the Oxford district are readily available in 

 the detailed reports of the Radcliffe Observatory, 2 taken over a period of 

 some seventy years, and few localities have been so thoroughly scheduled. 3 

 On the other hand, meteorological data are often singularly ineffective in 

 dealing with biological phenomena, owing to the particularly complex nature 

 of the problems, and the difficulty in making the most essential records. 

 Thus mere rainfall data arc of little use in themselves, without some knowledge 

 of the amount of water freely drained off, the humidity of the atmosphere, 

 and the deposition of dew on surface-vegetation. Probably hours of rainfall 

 would be more illuminative than a record of the actual amount. Similarly 

 the working value of sunlight in terms of intensity of photosynthesis bears 

 very little relation to the recorded ' hours of bright sunshine '. Where such 

 complex interaction of factors is concerned, the phenomena of plant-life, 

 as exemplified in delicate organisms to whom such factors are a matter of 

 life and death on a very narrow margin, probably afford a more reliable 

 guide than the efforts of the human observer in his attempts at the discussion 

 and tabulation of a few of the factors separately. 



I. Temperature. The mean maximum temperature of the air, obtained 

 by averaging the means for the 12 months, is 56-39 F. (for 70 years, 

 1851-1920), and the monthly averages may be expressed by a curve from 

 43-46 (January) to 70-67 (July). 



The corresponding minimum air-temperature is 49-45 F. ; from 34*37 

 (January) to 53-28 (July). This indicates on the whole a temperate climate, 

 but does not present the effect of either summer heat or winter frost. 



The highest air-temperature attained may be 94-7 F. (Aug. 9, 1911) ; 

 and 80-90 is commonly experienced on hot days in July, Aug., Sept. (91-6, 

 Sept. i, 1906), rarely in May (83-1, May 30, 1895; 85-5, May 22, 1921, 

 B. G. O.). The winter months (Jan., Feb., Dec.) rarely rise above 60 (61, 

 Feb. 10, 1899). Sun-temperatures may exceed 150 (rarely); 153-7, Aug. 9, 

 1911. 



Frosts may occur commonly in any month but June, July, and August ; 

 but exceptionally in June (28-6, June 25, 1918) ; while white frosts may occur 



1 Gunthcr (1913), Oxford Gardens, p. 155. 



1 Rambaut, Results of Meteorological Observations made at the Radcliffe Observatory, Oxford, 

 in g-yearly volumes ; Hi, 1916-21. 



1 Records of the Thames are taken in great detail by the Thames Conservancy : local data for 

 the Cherwell at Magdalen College Laboratory. Rainfall and temperatures at the Botanic Garden : 

 cf. Daubeny Reports, J. J. Manley, Magdalen College. 



