188 



PEPPER TREE AS A CAUSE OF HAY FEVER. 



from a mere inspection of the weather records, that there are 

 very few days in the other three towns when the temperature 

 and relative humidity approach those of the hot dry weather pf 

 November at Bloemfontein. But, as definite figures for the 

 drying of the pollen are not available as a basis of comparison, 

 it is impossible to be more precise. 



Table XIX. 



Summary of Weather in Five Towns during December, 1920, 

 WITH their Altitude and Average Barometric Pressure. 



The climate also affects the distribution of the j^ollen in 

 other ways. The moister the atmosphere, the earlier the flowers 

 fall. For example, with flowering shoots in water in a moist 

 atmosphere, more than one-third of thf^ flowers fall before any of 

 their anthers have dehisced. It is likely, therefore, that the 

 moister the atmosphere the smaller the proportion of pollen that 

 is blown directly from the tree into the air. Pollen starting from 

 the ground has, as already explained, a much more limited area 

 of distribution. 



Table XX. 



Summary of November Weather at Bloemfontein and 

 Kimberley. 



There is a striking parallelism between Bloemfontein and 

 Kimberley. Of the five towns investigated, they alone suffer 

 from this type of hay fever; in them alone is the pepper tree 



