170 PEl'l'Ki: THKH AS A CAUSK OF HAY FEVER. 



tors. If once pollen has been allowed to become really sticky, it 

 is not dried by lieating in an incubator in dry air at maximum 

 summer shade temperatures in Bloemfontein. 



If pepper tree pollen from a freshly opened anther be 

 examined under the microscope, it will be found that the grains 

 are stuck together by an oily yellow liquid. This liquid .is soluble 

 in ether and gives the other recognised reactions for essential 

 oils, and contains in solution the yellow pigment to which the 

 colour of the pollen is due. It seems probable that in cool moist 

 weather the essential oil is gradually changed to a resin, but that 

 in very hot weather it evaporates before this change can take 

 place, and hence the pollen becomes powdery. The weather 

 may also influence the nature of the oil formed by the phmt. 

 But, whatever be the reason, it is a directly observable fact that 

 in very hot dry weather the pollen becomes dry and~ powdery, and 

 so can be dispersed by the wind, whereas in cool moist weather 

 it remains sticky. 



The drying of the pollen in the hot dry weather, so charac- 

 teristic oi Bloemfontein during the epidemic season, is the ex- 

 planation why it is possible for the p.epper tree to cause hay- 

 iever. As far as I am aware, a similar change in the character 

 of pollen has not. been previously recorded ; nor has it been shown 

 that an insect-pollinated plant can cause hay fever to a serious 

 extent. 



My colleague, Mr. F. Zweerts, who has already had experi- 

 ence in research work on essential oils at ])elft, has expressed 

 the intention of investigating the question further next season. 

 The problem is a little research in itself. 



Some of the wind-blown pollen of the pepper tree must also 

 fall on the stigma of the flowers of this plant, but it is difficult 

 to gauge the importance of wind as an agent of pollination here. 



Incidentally, it may be mentioned that occasional grains of 

 the pollen of several cultivated insect-pollinated plants were 

 found on the pollen plates. On one occasion snapdragon pollen 

 was found on a plate suspended in a second floor window some 

 29 feet above the ground, and at a distance of some 110 paces 

 from the nearest snapdragon plant. It may be that many 

 pollens which remain sticky in the original home of the plant 

 become dry and are dispersed by the wind m very hot dry 

 climates. 



2. — Opcnuuj (uui SlifddiiKj of Floiver^. 



Usually, while the male pepper tree is flowering, the flowers 

 are continually being shed from it, and the ground beneath a 

 large male tree in full bloom is sometimes almost cream in 

 colour from the fallen flowers, which are shed, as a I'ule, soon 

 after opening, and whilst the petals are fresh and there is still 

 some pollen in the anthers. But, after a coiitinuance of hot dry 

 weather such as is prevalent during Novend)er and December in 

 Bloemfontein, flowers cease to be shed and the flower-buds re- 

 main \mopened on the trees. This liappened with some trees I 



