PATHOLOGY OF YOUNG TREES AND SEEDLINGS. 23 1 



The wall is thick, black, and hard and crust-like when the 

 perithecium is ripe. Plate XIV. Fig. 8 shows an empty 

 perithecium in section attached to the mycelium on a stem, and 

 in Fig. 9 one is seen in section partly embedded in a mass of 

 hyphae. Plate XV. Fig. 13 shows a section through several 

 perithecia still attached to the mycelial strands. The inner 

 surface of the wall, except for a small area near the opening, 

 is covered with a layer consisting of asci and paraphyses 

 (Plate XIV. Fig. 9). The paraphyses, which are colourless and 

 not easily seen in the ripe perithecium, are long and filamentous. 

 The asci are linear-cylindrical, 120-140 jx long and 8 /a wide in 

 the sporiferous part, and contain eight spores which are at first 

 colourless but become dark-brown when mature (Plate XVI. 

 Fig. 15). The wall of the ascus is colourless and, for the most 

 part, thin, but becomes much thickened near the apex, so that 

 the cavity of the ascus is here reduced to a very fine canal 

 (Fig. 16). This thickened portion takes up water readily, and 

 by its swelling the lumen of the ascus is completely obliterated. 

 On staining with iodine solution the thickened apex becomes 

 bright blue, a reaction characteristic of Rosellinia species (see 

 Fig. 17, in which the blue-stained apex is shaded). 



The spores, which are arranged in a single row in the ascus, 

 are spindle-shaped with pointed ends and, when examined 

 laterally, are seen to possess one flat and one convex side ; they 

 contain two oil drops and measure 18-20 x 7-8 /x (Fig. 18). As 

 in Rosellinia qiiercina there is a fine line on the flat side of the 

 sporC; extending over about seven-eighths of its length ; this 

 indicates the position of thickened ridges on the wall, and is 

 easily seen after the spores have been soaked for some time in 

 water (see Fig. 19; the upper spore is seen almost laterally, the 

 lower shows the flat surface in face view). 



There is considerable difficulty in the exact identification of 

 the fungus responsible for the disease. Although there is a 

 great resemblance to Rosellinia quercina the Scottish specimens 

 differ in several respects from the latter species. In the first 

 place, there is the question of host plant. Rosellinia quercina 

 has only been described on the oak in Germany, but in Denmark 

 it has been recorded by Rostrup ^ on the beech and sycamore. 

 There is no record of the occurrence of this species on conifers, 



^ Lind, Danish Fungi as represented in the Herbarium of E. Rostrup, 

 1913, p. 192. 



