PEPPER TREE AS A CAUSE OF HAY FEVER. 169 



All these insects when caught had a yellow powder sticking 

 to the body which, when examined under the microscope, proved 

 to be the pollen of the pepper tree. There is, therefore, no 

 reasonable doubt that the flowers are pollinated by insects (vidG 

 also the section dealing with the drying of the pollen). 



IX. Effect of the Weather on the Drying of the Pollen of 



Pepper Trees and on the Opening and Shedding of the 



Male Flowers. 



1. — Drying of the Pollen. 



In view of the fact that a preliminary examination of the 

 flowers of the pepper tree had shown that they had all the charac- 

 ters of typical insect-pollinated flowers (Potts, 1919), and, in 

 particular, had moist sticky pollen, it was a very great surprise 

 to find when pollen plates were exposed during the next avail- 

 able epidemic season that not only was pepper tree pollen present 

 in the air, but that it was there in large quantities. This neces- 

 sitated a re-examination of the flowers of the tree. This was 

 done in November, 1919, in hot dry weather, when it was found 

 that the pollen of many of the flowers still on the tree w^s dry 

 and powdery, and could easily be shaken out, and that the 

 anthers were in varying stages of emptiness, some being still full 

 of pollen whilst others w.ere nearly empty. Fallen flowers from 

 the ground yielded similar results ; those still fairly fresh con- 

 tained more or less pollen, whilst the dry withei'ed flowers, which 

 had presumably been longer on the ground, had empty anthers. 

 In other words, there was evidence in both cases of the gradual 

 disappearance of the pollen into the air. Also, if cut shoots are 

 placed in water in such w.eather the pollen gradually falls froixa 

 the anthers, and may be collected in considerable quantities. 



Further exf)erience showed that in cool, moist weather, the 

 pollen remains sticky, in fact, becomes increasingly so, whereas, 

 in hot, dry weather it becomes dry and powdery. When the 

 initial examination of the flowers w^as made in the autumn of 

 1918 the weather was cool and moist; and Bloemfontein was en- 

 joying a spell of the same kind of weather when it was necessary 

 to collect pollen for the purpose of the cutaneous tests. The 

 difficulty then experienced in separating the sticky pollen from the 

 flower has already been recorded (Potts. 1921), but it may be re- 

 coiled that this was finally effected by rolling the open male 

 flowei-s between sheets of plate glass to which the pollen adhered, 

 and from which it was removed with a razor. 



It is very difficult to separate the effect of heat from that of 

 dryness in drying the pollen under natural conditions in the open 

 air, as in Bloemfontein during the flowering season of the pepper 

 tree very hot weather is almost invariably parchingly dry. 

 Simple laboratory experiments also left considerable doubt re- 

 garding the question. They showed that a high temperature and 

 dry air are both favourable to the drying of the pollen, but ihat 

 the process seems to be complicated by other undeteiTnined fac- 



