PATHOLOGY OF YOUNG TREES AND SEEDLINGS. 229 



and Tubeuf,! in referring to this, states that when imported 

 infected trees were planted with healthy stock, full recovery of 

 the diseased stock resulted and the fungus did not spread to 

 the healthy plants. 



It therefore appears that, up to the present, no definite species 

 of Rosel'ifiia (with the exception of R. necairix) has been 

 described as causing a disease of the spruce. 



The fungus described in the present paper occurred on 2-year- 

 old plants of the common spruce {Picea excelsa) in a nursery in 

 the south of Scotland. Practically the whole of the plants in 

 the seed-bed were attacked by the disease. 



The plants when received were in a dying condition, but still 

 bore the brown discoloured needles. A superficial examination 

 shows that the lower part of the stem with the attached leaves, 

 and the upper portion of the root, are all more or less covered 

 with a greyish mycelium. This is scanty on the root but 

 increases in quantity on the lower part of the stem, while on 

 the lower leaves the hyphae are widespread, and sufficiently 

 numerous to bind them together in a mycelial weft (Plate XIII. 

 Figs. I and 2). In some cases a number of plants, which had 

 evidently been growing in close proximity, are connected 

 together by the very abundant development of the mycelium 

 (see Plate XV. Fig. 10, which shows the fungus in a later stage 

 of development). 



Microscopic examination shows that the hyphae, which are 

 colourless in the young condition near the growing points, 

 become brownish in the older portions. They differ considerably 

 in size, varying from 2-8 /i in diameter, but individual hyphae 

 are usually constant in width and only show the pear-shaped 

 swellings, characteristic of Rosellinia necatrix, to a very small 

 extent ; septa are fairly numerous and are at right angles to the 

 side walls, and clamp connections are not present- (Fig. 3, a, b) ; 



1 '■• Rhizoctonia violacea an Fichten," A^a/wrw. Zeitschr. Forst-u. Landw., 

 18, p. 233, 1920. 



■^ Clamp connections are small U-shaped branch hyphae which are 

 developed at the cross septa and connect up the cavities of contiguous cells ;. 

 they are characteristic of certain BasiJiomycetes, especially the Hymeno- 

 mycetes, and are not found in the Ascomycetes. Specimens of 4-year-old 

 plants of the Sitka spruce, showing oVjvious signs of disease, have recently 

 been received from Ireland, and in these a mycelium somewhat resemblin" 

 that of Rosellinia is present amongst the roots and on the stems and lower 

 leaves. This mycelium shows numerous clamp connections, and in con- 

 sequence cannot be assigned to any species of Rosellinia. 



