174 PETCH : 



the stroma is at first pycnidial and afterwards ascigerous. 

 When, both stages are produced in the same stroma, they 

 occur, as a rule, at the same time ; the stroma is both pycnidial 

 and perithecial. The pycnidia may be developed at the base 

 and the perithecia higher u}}, and in that sense the pycnidia 

 are the earlier ; but that arrangement is not universal. There 

 is, however, in the majority of cases, no ground for the assump- 

 tion that, as in so many other fungi, a pycnidial stage is 

 completed before the perithecia appear. Vestiges of effete 

 pycnidia are not usually found in the perithecial stromata, 

 though they may occur, and in some species, e.g^, Hypocrella 

 turbinata, may be a conspicuous feature. 



At present it is not possible to state what factors govern 

 the production of either stage. In one collection all the 

 stromata will be pycnidial, in another all will be ascigerous. 

 The combination of both stages in the same stroma is of rarer 

 occurrence, as would be deduced from the numerous descrip- 

 tions which refer to one stage only. This rarity, however, 

 may be more apparent than real, for in many cases it is not 

 possible to determine by mere inspection in what stage a given 

 stroma is. In the Lecaniicolous ppecies the perithecia and 

 pycnidia are scattered practically at random, and unless the 

 whole stroma is sectioned, it is more or less chance whether one 

 finds both the stages if they happen to be present. 



No evidence has been found in support of the statement 

 that the Hypocrella stage is developed after the leaves have 

 fallen to the ground. Under such circumstances the stromata 

 decay. It is not uncommon to find stromata in process of 

 decay on living leaves. 



Structure. 



Throughout the genera Hypocrella and Ascliersonia the 

 structure of the stroma is remarkably uniform. It is composed 

 of thick- walled hyphse, of piactically uniform diameter, but 

 intertwined without any definite direction, so that in section 

 one sees some hyphse in cross section as circular annuli, and 

 others in longitudinal or oblique section m short, straight, or 

 curved, or contorted lengths. The hyphse vary in different 

 species from 4 to 8 jji. in diameter ; von Hohnel lecords a diameter 



