HEART-ROT 101 
without at first becoming much thicker. If they are growing 
on the under-surface of a root they cling to the root until 
their width becomes greater than that of the root, when 
they grow beyond it in the shape of a bracket. If they are 
growing on the side of the trunk (always near the base) 
they develop the bracket form quite early. When these 
fructifications reach the size of a penny, and sometimes 
much earlier, pores or slight depressions appear on the 
lower surface. These are the beginnings of the tubes inside 
which develops the hymenial surface. The fructification is 
then composed of a continuous layer of hyphae on the 
upper side, about 1-2 mm. thick, and a layer of vertical 
tubes on the lower side, which may be more than double 
this thickness. The upper surface is at first pale brown ; 
in resupinate fructifications it remains pale, but in bracket 
fructifications it becomes darker, until it attains a dark 
reddish-brown colour. As long as the fructification is 
growing laterally the margin is white (fig. 40), but when 
lateral extension ceases the margin generally becomes 
dark brown like the rest (fig. 29). This surface is concen- 
trically turrowed (at any rate in bracket forms), and the 
furrows are striated radially. The lower surface is at first 
white, and may also be pure white in older fructifications, 
but it often becomes biscuit coloured and even slightly 
reddish, especially at times when it is not growing actively. 
The fructifications grow in size (i) by the tubes becoming 
longer, thus increasing the thickness, and (ii) by marginal 
growth, which makes the fructification broader. The new 
parts bear pores very nearly up to the margin, and the 
youngest portion is always the whitest. Fructifications 
may reach a considerable size, and the largest I have seen 
is 17-5 by 8-5 in. and 5 in. thick. This specimen, which is 
shown in figs. 29 and 30, was found by my wife on a dead 
spruce. Growth is most active in summer, but I have 
found fructifications growing vigorously and bearing spores 
in March. When growing, the marginal extension keeps 
somewhat ahead of the pore-formation, so that the margin 
is sterile, but as soon as marginal growth ceases, pores are 
