394 SECTIONAL TRANSACTIONS.— K. 



Dr. J. F. V. Phillips.- — Some Important Vegetation Communities in the 

 Central Province of Tanganyika Territory. 



The Central Province — its northern boundary lying between 4° and 5° S. lat. 

 approx., its southern limit the Ruaha-Nzombe river (7° S. lat. approx.), bounded on 

 the east by a line ranging between 36° 3' and 36° 5' E. long., and with its western 

 limit varying between 33° and 34° E. long. — forms portion of the great central plateau 

 of Eastern Central Africa. Represented are elevations from 3,000 to 6,000 feet, the 

 bulk of the country lying between 3,500 and 4,500 feet. The country rocks are 

 granite, gneiss and crystalline schist. Important soils are the eluvial red and grey 

 sandy-loams and clays and the alluvial red and grey sandy-loams and clays. 



The rain-bearing winds are local and variable. The mean annual precipitation, 

 based upon all too meagre data, perhaps, has as its limits 300 and 1,000 mm. The 

 ' short ' rains fall between late October and late December with a variable dry spell 

 in January and part of February, the heavier fall (' long ' rains) being during March, 

 April, and a portion or the whole of May. 



Critical temperature data are wanting, but it seems that the mean annual air 

 (shade) temperature as obtained in Stevenson screens ranges between 18° C. and 

 23° C, according to locality. 



A knowledge of the nature and relations of the principal vegetation communities 

 is indispensable to a better understanding of (a) the conservation of the soils, (6) the 

 regulation of grazing, (c) the habitat relations, control and combat, of the tsetse-flies, 

 Olossina morsitans and G. swynnertoni. 



The aim is to record preliminary impressions of some of the more important 

 communities and to suggest certain of their relations. More critical information is 

 being obtained by quantitative instrumental and quadrat methods. 



The communities fall readily into the following main classes : — 



1. Open grass, short or long, without incipie^it or relict (fire) largely-deciduous, 

 thicket elements. 



2. Open grass, short or long, with incipient or relict (fire) largely-deciduous, thicket 

 elements, scattered or in communities of variable density and extent. 



3. Acacia open-woodland communities, grass-growth variable, often tall. 



4. Combretum-Other spp. open-woodland communities, grass-growth variable, 

 often tall. 



5. Largely-deciduous thicket in which Commiphora spp. and other spined or rigid 

 woody shrubs play an important part ; grass-growth either absent or verj^ sparse. 



6. Deciduous thicket in which Grewia spp., Baphia, Bussea, Pseudoprosopis and 

 trailing Combretum are the important forms ; grass-growth either absent or very 

 sparse. 



7. Berlinia-Brachystegia-Other spp. woodland ; grass-growth variable, depending 

 upon soil moisture. 



8. Upland Brachystegia (microphylla) Other spp. woodland. 



9. Sub-tropical Evergreen Scrub, transitional to sub-tropical Evergreen Forest ; 

 in highlands above 5,000 feet. 



10. Sub-tropical Evergreen Forest, upon moister highlands above 5,000 feet. 

 Within these classes the principal communities are listed and described briefly. 



Dr. S. ScHONLAND. — Some South African Plant Hybrids and the Bearing 

 of our Knowledge of Plant Hybrids on the Theory of Evolution. 



To deal with this matter one must make it clear what one means by Hj^bridisation 

 and incidentallj' what is meant by a species. Nobody has as yet been able to 

 satisfactorily define what a species is. This is only to be expected, as species are 

 onljr subjective conceptions and do not exist in nature. Damin's recommendation 

 has worked well in practice. He said : ' Sj'stematists wUl have to decide whether 

 any form is sufficiently constant and distinct from other forms to be capable of 

 definition and, if definable, whether the differences be sufficiently important to 

 deserve a specific name.' Many hybrids are the result of crosses between individuals 

 of different species. These may be called interspecific hybrids. In view, however, 

 of the fact stressed by Lotsy that in nature no homozygotes occur (he despairs even of 

 ever creating one artificially), the crosses between the individuals of any heterozygous 

 species must also be looked upon as hybrids. The writer designates these 

 intraspecific hybrids. If interspecific hybrids can and often do represent or lead to> 



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