PEPPER TREE AS A CAUSE OF HAY FEVER. 



189 



numerous and dense ; and they are the only towns in which 

 pepper tree pollen was found in the air. They also agree in having 

 a similar climate, and one that is very different from that of any 

 of the other three towns. Their weather in the early summer 

 is much hotter and drier, and more windy and dusty. The large 

 number of pepper trees produce a correspondingly great amount 

 of pollen, and at the season when the trees are flowering most 

 profusely and producing pollen in the greatest quantity, the 

 weather is such as to make it powdery, winds to disseminate it 

 are frequent, and it falls on mucous membranes made unduly 



Table XXI 

 Eaixfall. 



The average rainfall at Grahanistown is 28.79:n. and at ]\Iaritzburg 3o.79in. 



sensitive by drought and dust. Climatic factors, therefore, seem 

 to play a large part in making possible and aggravating the 

 disease. To the climate, too, the preponderance of pepper trees 

 in Bloemfontein and Kimberley is, I understand, to be 

 attributed. When street-planting, on a large scale, was under- 

 taken in these towns, this tree was one of the few known to 

 grow well on the streets. In the other towns, several varieties of 

 street tree grow well; there is therefore a smaller proportion of 

 any one kind in the town. 



It seems likely that the male pepper tree would cause hay 

 fever to a serious extent in towns where the tree is vei-y dense, 

 and where the climate is very hot and dry during its principal 

 Howering season. The degree of heat and dryness would probably 

 need to be something approaching that of Bloemfontein and Kim- 

 berley during November and December. Such a climate during 

 the flowermg season of the pepper tree occurs over the southern 

 and w^estern part of the Free State, and over the bulk of the 

 northern, central and w^estern parts of the Cape Province. 



In this area, male trees around isolated houses would also be 

 expected to cause hay fever in susceptible occupants. The hay 

 fever prevalent in Bethulie, Brandfort, and certain other small 

 towns in this region, which have pepper trees, is probabl}' due ro 

 this plant, though there has not been an opportimity of determin- 

 ing the varieties of pollen in the air of these towns. These small 

 towns are very scattered, and it is probable that the density of 



