New Phdma Disease of the Swede. 



449 



A 



Fig. 2. — Features of the commencement of the attack. A — Soon after infection. B 

 and C — Somewhat later. In C the rind is peeling off. and .the pycnidia are 

 already appearing beneath it. From Cockle Park. Nat. size. 



spreading transversely rather than vertically, and soon the 

 external corky layer cracks in the centre Fig. 2 B ; in a 

 somewhat later stage it becomes further torn apart with a 

 tendency to peel off in flakes Fig 2 C , and at this time, too, 

 numerous small black dots pycnidia appear. As the 

 disease spreads the tissues rupture more completely, the 

 crack extends in the direction of the longer axis of the 

 diseased area, and gradually deepens and widens- 

 till great dry fissures are produced, such as are 

 seen in Fig. r. A vertical section through a similar fissure 

 measuring 1 1 cm. in length showed it to penetrate to a 

 depth of 4 cm. One striking- characteristic of the disease 

 is the dry condition of the attacked cells ; the rind easily 

 separates as a dry papery layer. This drying up of the cells 

 is apparent in the very initial stages by the sinking in to form 

 a slight depression, and later on is more strongly marked by the 

 further shrinkage following upon the entire collapse of the 

 cells, and the formation of deeper hollows and the large 

 fissures already described. 



Such is a description of the external features of the disease. 

 An examination of the internal tissue? by the microscope 



F F 



