AEROBIOLOGY 



allergens, and may throw light on the causes of some of the seasonal 

 asthmas — especially those of late summer whose etiology is unknown 

 (Maunsell, 1958). The purest air appears to be just above the ocean, 

 though life on board ship has its own allergic hazards. 



PALYNOLOGY 



Pollen statistics, pollen analysis and, more recently, palynology, are 

 various names given to a group of studies including investigation on the 

 ecolog)', vegetation, and pre-history of the Quaternary Period by examina- 

 tion of the pollens preserved in peat and other deposits. Palynologists 

 have contributed considerably to the development of aerobiology, and 

 are well aware of the complications of wind-borne pollens from distant 

 sources (e.g. Buell, 1947). The problem is one of sampling in a given 

 locality, so as to eliminate uneven distribution from the dominating in- 

 fluence of one near-by source. 



We still need to know how the total deposit at one point is made up of 

 the few local distributions plus the tails of the distributions of many 

 distant sources. Furthermore, we must expect that sometimes an active 

 re-concentration in a cloud may reverse the diffusion process, and may 

 lead to the kind of incident \^■hich Pettersson recorded with a heavy 

 shower of Aloina spores. How far re-concentration in the air needs to be 

 taken into account, and how far surface obstacles may lead to local deposi- 

 tion, is a matter for studv. 



Spores and pollen preserved in glacial ice in mountainous and polar 

 regions offer scope for investigation that is still almost unexplored (cf. 

 Vareschi, 1942). 



EVOLUTION 



It seems that in each locality or habitat, mutation and recombination 

 are apt to act, through selection, to evolve special local divergent popula- 

 tions. But, simultaneously, dispersal mechanisms tend to counteract 

 this process by encouraging outbreeding and so increasing uniformity. 

 How the two processes balance is a genetical problem depending on 

 external factors and on the breeding systems involved. Aerobiolog}' con- 

 tributes quantitative information on the size of the breeding group, which 

 must be determined partly by the characteristics of the dispersal gradient. 

 Wind-borne genes are not distributed 'normally' (in a statistical sense) 

 around their point of origin but in a characteristic hollow curve, which 

 has the interesting property of involving greater frequencies near the 

 source and at great distances (at the expense of intermediate distances) 

 than if the genes followed the normal frequency distribution. 



Over the greater part of the Earth's land surface the ecologically 

 dominant flowering plants and conifers belong to wind-pollinated (anemo- 

 philous) species. Temperate and tropical grasslands, coniferous forests 



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