Daldinia concentrica. J. S. Bayliss Elliott. 271 



exterior is brown in colour and it only becomes black when it 

 ceases growth; at this stage the whole stroma is exceedingly 

 brittle and carbonaceous especially the exterior layer, about 

 •5 mm. in thickness, which is so hard that it is difficult to force 

 even a sharp needle through it, but the interior remains quite 

 soft and has a somewliat fibrous texture. The zoning so charac- 

 teristic of this fungus is due to the formation of successive layers 

 of perithecia. Perithecia are continually being formed in the 

 stroma just immediately beneath the thin hard external layer 

 (fig. 36); they are to be seen even in stromata of 3 or 4 mm. 

 diameter but only those of the last formed zone reach maturity; 

 the outlines of previously formed perithecia (fig. 34) are to be 

 observed more or less distinctly in the zones near the exterior; 

 these are easily recognised because the hyphae forming the walls 

 of the perithecia turn black some time before the hyphae which 

 form the bulk of the stroma. 



Although actual experiments were not carried out, from various 

 observations there seems reason to believe that the periods of 

 perithecial maturation correspond with periods of diminished 

 humidity while increase in humidity brings about active growth 

 which ultimately leads to the formation of a new perithecial 

 zone and atrophy of the perithecia of the preceding zone. 



It is quite recognisable that the fibrous nature of the interior 

 of stromata is due to these perithecia which never attain ma- 

 turity: some zones in consequence of the perithecia having 

 attained quite an advanced stage of growth before renewed 

 growth of the stroma occurred have quite a porous appearance 

 owing to the numerous large sterile perithecial cavities there. 



Although in section mature stromata look a smoky-brown 

 colour, while growing the last four or five zones are seen to be 

 zoned alternately black and white: the black zones owe the 

 dark appearance to the abundant perithecia there, the walls of 

 which are always nearly black (fig. 34). 



The hard exterior is exceedingly protective for a stroma 

 becomes immediately mined by slugs when cut, or after being 

 cracked by frost : the stromata crumble away during the winter 

 and so do not last more than one year. 



Very young stages in the formation of perithecia are difficult 

 to observe because they are formed close under the dark brittle 

 protective outer layer of the stroma: in the youngest which 

 could be clearly distinguished small spherical masses of hyphae 

 (figs. 38, 39) were seen which consisted of an external covering 

 tissue of densely woven, very narrow, thin walled hyphae, 

 surrounding a central hyphal mass of very wide septate hyphae : 

 the latter formed an irregular coil of several turns and doubtless 

 functioned as ascogenous hyphae: \ery similar structures are 



U.S. ' 3 



