I 1 6 TRANSACTIONS OF ROYAL SCOTTISH AKBORICULTURAL SOCIETY. 



The perithecia ripen in April or May. They probably appear 

 in the previous autumn, but their development has not been 

 completely followed, as, in the early stages, they closely resemble 

 immature pycnidia. When mature the perithecia are globose 

 or slightly ellipsoidal and bluntly conical in the upper part; 

 they measure 150-200 // in diameter; the wall is thick (37-43 /^) 

 and consists of dark-coloured, almost opaque, hexagonal cells. 



The perithecium is completely embedded, and during its 

 development pushes up the overlying tissue (Fig. 5). At 

 maturity the upper conical portion is covered only by the 

 epidermis or cuticle, and, in consequence, the dark colour of 

 the wall is easily seen. The asci arise from the base and 

 completely fill the perithecium, except for a plug-like mass of 

 yellowish cells, which occupies the upper part (PI. V., Fig. 8). The 

 perithecium opens by a rather irregular rupture and, at the same 

 time, the overlying epidermis is split, disclosing a small portion 

 of the wall. There are numerous asci in the perithecium, about 

 10 or 12 being seen in a median section (Fig. 6). The asci 

 are club-shaped or fusoid, with a short stalk ; the measurements 

 given by Bubak are 50-90 x 20-22 /x, but the Scottish specimens 

 are slightly smaller than this, the average size being about 

 65x20 /x (Fig. 9). Paraphyses are absent. The number of 

 spores in the ascus is unusual, varying from 16 to 25 (according 

 to Bubak, 10 to 24), the average being about 18 ; the spores are 

 irregularly arranged and closely packed in the ascus ; they are 

 two-celled, scarcely constricted at the septum, ellipsoidal; as 

 arranged in the ascus, the upper cell is broader than the 

 lower; the upper end of the spore is rounded, the lower being 

 acute ; the spores are hyaline, measuring 10-21 x 4-6 /x (according 

 to Bubak, 13-21 x 5-6 /x). 



The cause of the death of severely attacked branches during 

 the summer is still somewhat doubtful. By sectioning, it was 

 ascertained that hyphae of the fungus, although abundant in the 

 bases of diseased leaves, do not pass into the stem in the earlier 

 stages of the disease. They were found, however, in A. pectinata 

 in stems of the current year in the early part of September. 

 These stems were dead and the tissues were completely dis- 

 organised. In both A. pectiriata and A. nobilis sections taken 

 below the region bearing diseased leaves show yellowing of the 

 cortical tissues, but no hyphae are present. The discoloration 

 increases as the part of the stem bearing diseased leaves is 



