8o 
W. Watson. 
there was a slight increase in December and an apparently stationary 
condition in January prior to the early vernal maximum (January 
to March) which followed. 
The Protococcales and Ulotrichales are dominant somewhat 
prior to the Conjugate and Heterokontse, the Conjugatae dominating 
every other form in April and May. One species of Spirogyra has 
been described which is apparently a summer form. 
Some attempt has been made to elucidate the complex causes 
underlying the distribution and periodicity; but our knowledge of 
the habits of most of the algae is too limited to throw very much 
light on such problems. Further observations are in progress with 
a view to obtaining more detailed information on various points. 
In conclusion, I have to acknowledge the valuable help of Miss 
Winifred Blackwell, formerly a student of Westfield College, in 
collecting and examining some of the samples of 1912. I am also 
indebted to her for one of the July records of 1913. My thanks 
are also due to Professor G. S. West for kindly looking through 
some of the material, and for identifying the species of Spirogyra, 
Microspora, Ulothrix and Tribonema recorded. 
A SOMERSET HEATH AND ITS BRYOPHYTIC 
ZONATION. 
By W. Watson, B.Sc. 
[With Seven Figures in the Text]. 
I. Introduction. 
WET heath association is well shown on a portion of Chard 
Common in South Somerset. The dominant vascular plants 
are Molinia coerulea, Erica tetralix and Myrica gale, and these 
occur in a field of about 3 acres (F2 hectares) on siliceous Mid- 
Lias beds, the field having an altitude of about 350 feet (106 metres) 
above sea-level and a fairly regular slope of about 1 in 30). Along 
two sides of the field there runs a stream fed by many small 
tributaries, which in turn are fed by the water from the furrows 
between the Molinia tussocks so that a network of small potential 
