BOTANY 49 



edaphic succession, and that woodlands, and perhaps all 

 natural plant communities, tend to pass from a basic to an 

 increasingly acid condition with resultant changes in their 

 flora. This may explain not only the depression of the upper 

 woodland limit in this country, but also some of the plant 

 successions observed in peat. 



Exceptions to the normal gradient occur where the subsoil 

 is rich in bases and the manurial action of the leaves, etc., 

 enriches the topmost layer. In general, buffer action is greatest 

 at the surface where there is the greatest stability of reaction. 

 With the same species and on the same type of soil there appears 

 to be a fairly close relation between the organic content of the 

 soil and the real acidity. 



This stratification is reflected in the vertical distribution 

 of the micro-organic population of the soil and in the character 

 of the vegetation as a whole. 



Atkins {Proc. Roy. Dublin Soc, xvi), in a paper dealing with 

 soil acidity, gives data respecting the reaction in various types 

 of vegetation. Thus a sand dune with Salsola kali gave p.H. 8-4. 

 An older grassy phase gave j-2-y'2>. Soil with Ulex europceus 

 gave a range of 5 -4-8 -6 in 27 localities. Silene maritima 

 6-0-7-8 (7 loci), Rubus fruticosus $-4-8'4 (17 loci), Pteris 

 aquilina 5 •0-7-6 (10), Erica cinerea 4-6-6-0 (6), Calluna vulgaris 

 4-6-5-8 (6), Digitalis purpurea 5*4-7-2 (2). 



The effect on the growth of various tree seedlings of three 

 types of soil, namely sand, sand + humus, pure humus 

 with and without addition of lime, has been studied by Barring- 

 ton Moore {Ecology, Sept.). The species used were Pinus 

 rigida, P. Banksiana, P. resinosa, and Thuja occidentalis . As 

 might be expected from its nitrogen content, growth was 

 greatest on the humus soil and least in the pure sand, but the 

 important result of the experiment was that even light liming 

 had a detrimental effect on all the species mentioned. 



The vegetation of S.E. Missouri is briefly described by 

 Uphof in the Amer. Journ. Bot. The annual rainfall is high, 

 I-I-I-5 in., whilst the climate is characterised by hot summers 

 (max. over 40° C.) and mild winters (min. — 5° C). 



The forests consist chiefly of Oak, of which several species 

 are important. On the drier and less fertile soils, Q. marilandica 

 is predominant. Herbs with storage organs, e.g. Podophyllum 

 peltatum, are a feature of the ground flora. 



The more fertile soils with higher water content bear woods 

 of Q. alba and Q. rubra, with numerous associated trees and a 

 shrub layer also rich in species as in individuals. The moister 

 parts of these woods are the especial home of Impatiens fulva, 

 now so abundant an alien by canals in this country. 



Limestone outcrops are marked by pure stands of Juniperus 

 4 



