HEART-ROT 101 



without at tirst becoming much thiclvcr. If they arc growing 

 on the under-surface of a root they chng 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 

 wliich develops the hy menial 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 sm-face 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 hke the rest (fig. 29). This surface is concen- 

 trically furrowed (at any rate in bracket forms), and the 

 furrows are striated radially. The lower surface is at first 

 white, and may also be pm'e 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 ujj 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 1 have 

 found fructifications growing vigorously and bearing spores 

 in March. When growing, the marginal extension keeps 

 somewhat ahead of the i)ore-formation, so that the margin 

 is sterile, but as soon as marginal growth ceases, pores are 



