172 PEPPER TUEE AS A CAUSE OF HAY FEVER. 



is favourable to their oj^eniiig. When such a shoot with open, 

 flowers is very «lightly shaken, as would be caused in nature 

 by a light breeze, the open flowers fall freely. 



Further observation confirmed the original experience, but 

 also showed that all the trees of a neighbourhood do not 

 cease to shed their flowers at the same time. Thus, after a con- 

 tinuance of hot, dry weather, large trees which, presumably, 

 have access to water — for example, in some gardens — continue to 

 shed their flowei's for several days after the smaller, less fav- 

 oured trees — for example, growing on the streets — have ceased 

 to do so. 



In the case of the female tree, only the petals and stami- 

 nodes are shed, and, as these organs are very small and each 

 falls separately, they are not noticed on the ground. 



In response to a circular letter distributed to epidemic suf- 

 ferers in Bloemfontein regarding tlieir experiences, it was noticed 

 that, whilst many expressed the opinion that rain gave them 

 relief, about an equal number stated that their symptoms were 

 aggravated after rain. The former experience was only to be ex- 

 pected, as rain is understood to wash pollen out of the air and 

 to wa«h away or, at least, lay the dust. The latter opinion, 

 though, is surprising and unusual, I believe, but it was expressed 

 by so many sufferers, and frequently with such conviction, as to 

 leave no doubt that there must be a basis of truth in it. The 

 observations regarding the opening of the flowers suggest an 

 explanation. A light shower after a continuance of hot dr,y 

 weather may allow the flowers to open, and so increase the 

 amount of pollen in the air, and thus aggravate hay-fever sj'mp- 

 toms ; whilst a heavy rain, by washing the pollen from the air 

 and dust from the streets, and by causing a short spell of cool, 

 moist weather, and therefore sticky pollen, gives temporary 

 relief. 



The observations may also explain the absence of pepper- 

 tree pollen from the pollen plates in hot, dry, windy weather, 

 that seems suitable for the dispersal of this pollen ; the flower buds 

 may have ceased to open. In cool, moist weather, the flowers 

 open, but the pollen remains sticky. After a long spell of liot, 

 dry weather, the flower-buds cease to open, so that in neither 

 case does the pollen find its way into the air. It seems probable. 

 in the light of these observations, that the greatest amount of 

 pollen would be expected in the air in hot, dry. windy weather, 

 with occasional light showers. The showers allow the flowers 

 to open, the hot, dry air dries the pollen, and the wind can then 

 disseminate it. In point of fact, meteorological records show 

 that this is the kind of weather usually prevalent in Bloemfon- 

 tein durinp- the epidemic season, though we seem to hardly 

 notice the light showers (rude Table III). 



How much of the pepper tree pollen floating in the air 

 comes directly from the trees, and how much from the flowere 

 after they fall, cannot be estimated. 



