PEPPER TREE AS A CAUSE OF HAY FEVER. 177 



less windy. Soft balmy breezes replaced the hot, dry, 

 parching, westerly wind. There was also very little dust. In 

 fact, the weather was distinctly pleasant. There was also very 

 little hay fever, and the cases were mild in type as compared 

 with those during the epidemic season. The weather, state of the 

 vegetation and position regarding hay fever as just described, 

 are fairly typical for this period of the year in Bloemfontein. It 

 was the rainy season, and good growing rains had fallen at suf- 

 ficiently short intervals to keep the natural vegetation (grass) 

 growing vigorously and allow it to flower. 



It is concluded that the little hay fever about was attribu- 

 table to grass pollen. Some of the patients now suffering also 

 suffer during the epidemic season; others are free from the 

 trovible until the grass begins to flower. The conclusion is drawn 

 that the former are susceptible to both pepper tree pollen and 

 grass pollen, whereas the latter suffer from grass pollen but not 

 from pepper tree pollen. 



From Table II it will be seen that 16.36 inches of rain fell 

 at Bloemfontein diu'ing the first three months of 1920, as com- 

 pared with 4.41 for the preceding eight months. This should be 

 kept in mind in comparing the results shown in Tables IV and 

 XIII. The contrast in the rainfall of the dry and wet seasons 

 in this case is more marked than usual, partly no doiibt because 

 1919 had the lowest rainfall ever recorded for Bloemfontein 

 (11.64 inches). 



XII. Difficulties in Accepting the Pepper Tree as a 

 Cause of Hay Fever. 



There are three main difficulties in accepting the pepper tree, 

 as a cause of hay fever in nature : (1) it is insect-pollinated ; (2) 

 the relatively large size of its pollen ; and (3) the fact that the 

 tree occurs in other towns of the Union which are not seriously 

 troubled with hay fever. These objections will now be considered 

 in turn. 



(1) Insect-pollination. 



All the plants which have hitherto been shown to cause hay 

 fever on a large scale are wind-pollinated, and a perusal of hay 

 fever literature shows that it is an accepted principle that only 

 such plants can cause the affliction. The explanation of the 

 anomaly in the case of the pepper tree is, that in very hot, dry 

 weather, such as is frequent in Bloemfontein in November and 

 December, the pollen, which is naturally sticky, becomes dry and 

 powdery and so can be earned by the wind. 



(2) Size of Pollen. 



It has been shown that a small particle such as a pollen 

 grain, whilst being carried by the wind is really going through a 

 process of falling, and that it is doing so with a uniform velocity 

 rather than an acceleration. The relative velocity of fall of 

 smooth spherical pollens through the air may be taken, for prac- 



