552 



DIE-r.ACK OF APPLE TREES. 



except for the younger branches, is brown in colour. It is 

 richly branched and closely septate. The individual cells, which 

 are vacuolate, are from 13.2 — 39.6/x long. Mycelial threads 

 running close together are frequently united by cross-connections 

 (Fig. 2). 



The pycnidia, as noted above, are either single or aggregated 

 together. Of the latter, there appears to be two types: (i) The 

 pycnidia, while each having their own wall are enclosed in a 

 common wall, and may thus be said to be borne in a stroma. 

 The walls separating individual pycnidia become confluent, much 

 as occurs normally on the host-plant. (2) The pycnidia, while 

 aggregated together and with thick walls, are not enclosed in a 

 common wall (PI. 23, c). May be this condition is ai^parent 

 rather than real, and results on the way the sections are cut. 

 The above types are found at 25° C. 



Fig. 3. 



At 30° C. the pycnidia ap])ear to be always single, and the 

 walls thin (PI. 23, d). This tyi)e also occurs at 25° C. The 

 spores (Fig. 2) are minute, hyaline, allantoid, and measure 

 4.62 — 6.16 X I-54M- 



Turnip tubes (Fig 3). — At 30° C. the fungus, Vvnthin five 

 days, formed a vigorous flat, greyish growth, which after eleven 

 days was an ashy grey, and just above the cotton wool and 

 along the glass a madder brown. Where medium fungus and 

 glass met, the colour was of a dark neutral tint. After one 

 month the growth was a mouse colour, with a dark neutral tint 

 above the cotton wool. Cutting the turnip through, it was seen 

 to be dark red all over. Small ]:)ustules containing spores 

 were evident on the surface, and raised, hummock-like bodies, 

 containing pycnidia, were also present. 



