450 SECTIONAL TRANSACTIONS.—K. 
I :20,000 has rarely been possible or attempted, but the production of wide 
angle lens and multi-lens cameras on a commercial rather than on an experi- 
mental basis is imminent, and it may be predicted that small-scale photo- 
graphy will shortly be possible in many circumstances at a cost not exceeding 
one halfpenny per acre. 
Dr. G, F. Asprey.—The effect of washing on the subsequent absorption and 
exosmosis of electrolytes by potato tissue (11.0). 
When discs of potato tuber tissue are washed in running tap-water for 
periods varying from 24 to 120 hours it is found that their subsequent 
exosmosis into distilled water varies inversely as the length of the washing 
period. ‘The subsequent absorption of ions from ammonium chloride 
solutions by similarly treated tissue, on the other hand, varies directly 
as the duration of the previous washing. It would seem then that high 
absorption of ions by the tissue is associated with low outward diffusion of 
electrolytes. ‘This conclusion is contrary to expectations based on ionic 
interchange, nevertheless it is confirmed by experiments in which are 
ascertained both exosmosis into, and absorption of ions from, ammonium 
chloride solutions by differentially washed tissue. The bearing of these 
results on our knowledge of the process of salt intake is considered. 
PRESIDENTIAL AppreEss by Mr. F. T. Brooxs, F.R.S., on Some aspects of 
plant pathology (12.0). (See p. 169.) 
AFTERNOON. 
Joint Discussion with Department K* (Forest and Section M 
ry 
(Agriculture) on The utilisation of light land, with special reference to 
Breckland (Section K room) (2.0). 
Dr. A. S. Watt.—The climate, soil, and vegetation of Breckland. 
Breckland is a well-defined physiographic unit, whose vegetational 
features are determined by a dry soil in a dry climate. The significant 
climatic factors are thrown into relief by a comparison of the meteorological 
data from places with an oceanic and sub-continental climate respectively. 
This brings out the combination of the relatively high summer temperature 
with a summer rainfall which is absolutely low. Other important factors 
_are the high number of hours of sunshine and the shortness of the frost-free 
period. 
There is a wide variety of soil type from calcareous shallow soils through 
deeper soils deficient in calcium carbonate to very acid heavily podsolised 
soils. Wind erosion has played and still plays an important part ; some 
soils are maintained in an immature state ; podsols have been truncated to 
different levels, whilst the soil which has been removed forms a blanket of 
varying thickness over much of the area. Thus the soils vary much in 
chemical, less so in physical properties, for (with some exceptions of small 
extent) all are highly permeable with a small water retaining capacity. 
The flora, under this combination of dry soil and dry climate, is essen- 
tially drought resistant or drought escaping. But while dry conditions 
stamp the vegetation as a whole, vegetational variation closely follows 
physical and chemical variation in the soil. The chief vegetational types 
are mentioned and their relationships outlined. 
