38 



THE LARCH CANKER 



A section through a ripe apothecium shows the lower 

 portion, or excipulum, differentiated into two parts. The 

 outer (lower) portion, or cortex (fig. 17, c), is composed of 

 a mass of closely interwoven and rather swollen hyphae of 

 firm texture. The middle portion is made up of hyphae 

 which are much less closely interwoven. The hard cortex 

 not only prevents loss of water from the apothecium, but 

 also assists in closing it in dry weather. For on drying the 

 central portion contracts more than the cortex, and this 



FlQ. 17.— Section through apothecium of Dasyscypha calycina: c, 

 cortex ; h, hymenial layer ; s.l, subhymenial layer. 



causes the margin to fold over the hymenial layer (figs. 

 15 and 16). 



The hymenium (fig. 17, h) is a layer composed of asci 

 and paraphijses, and is borne by a dense subhymenial 

 layer, s.l. The details of the hymenial layer are more clearly 

 shown in fig. 18, a. The ascus, a, is the organ which pro- 

 duces and ejects the spores. The eight spores occur in 

 a single row and fill the upper part of the ascus, whilst the 

 lower part contains hyaline protoplasm. The length of the 

 ascus is 150-200/^, and the greatest breadth is 10-14 m. It 

 is nearly cyhndrical, but somewhat swollen towards the 

 upper end, and tapering at the lower end. The walls are 

 sufficiently thick to show a double outline under a D objective, 

 except at the extreme apex, and are quite smooth. The 

 spores (fig. 20, a) are ellipsoidal, the long axis being 2 0-23 f/, 



