Further Observations on Heath Association. 129 
adventitious roots from the branches in contact with the soil. A 
unique instance of the prostrate type is afforded by the young plants 
of Pinus sylvestris in which the main axis appears to have been 
bitten off by rabbits, whilst the laterals, probably under the influence 
of the wind, continue for a time to grow horizontally (PI. I, Phot. 1). 
Of the numerous young trees of P. sylvestris on the land-slides 
several show that they possessed the same prostrate habit in young 
stages, the present main axis being one of the laterals that has 
assumed a vertical direction. 
The effect of nibbling upon the Calluna is very striking, and 
results in extremely dense branching which, in the case of the more 
erect specimens, gives the plant the habit of a Japanese dwarf tree 
(PI. I, Phot. 2). Where old cushions of Ulex europteus , bitten in 
this way and simultaneously subjected to considerable exposure, 
have grown in the upward direction, the cushion-habit is retained 
throughout, whereby various grotesque forms are assured (PI. I, 
Phot. 6). 
C.—Colonisation. 
(1) Cryptogamic succession. 
Amongst the first new arrivals to appear on a burnt area are 
algae. These are Cystococcus humicola Naeg., forming dark green 
granules in most of the countless small depressions of the soil, and 
gelatinous forms ( Glceocystis vesiculosa Naeg., Trochiscia aspera 
Hansg. and Dactylococcus infusionum Naeg. 1 ) constituting a thin, 
macroscopically invisible layer over the greater part of the surface. 
At a very early stage Ascobolus atrofuscus 2 is to be found growing 
over the whole gelatinous layer, its hyphae ramifying profusely in 
the latter and especially enveloping groups of the Cystococcus in a 
dark pseudoparenchymatous investment. These enveloped groups, 
when viewed with a lens, appear as numerous minute rounded 
protuberances of an olive-brown colour which, when present in 
large numbers, give a velvety texture to the surface. The apothecia 
arise in quantity from the hyphae generally and do not seem to 
develop from the threads more intimately associated with the 
Cystococcus. The same fungus is common on burnt areas of all 
ages, as well as on parts of the mature heath. Another fungus, 
rare and local in its distribution, is Humaria melaloma which has 
only been encountered on one of the burnt areas in the early part 
of the year. 
1 This is generally regarded as a stage of Sccnedcsmus obliquus Kuetz. 
5 For the identification of these Fungi, the authors are indebted to 
Mr. J. Ramsbottom, M.A., and for the identification of Mosses to Dr. F. Cavers. 
