200 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



and Fig. 4). Occasionally two adjacent pseudoperidia become 

 partially or completely fused together (Fig. 2). The wall of the 

 pseudoperidium is one cell in thickness, the cells being rhomboi- 

 dal or polygonal in shape and the walls finely verrucose (Fig. 

 7). The numerous spores are orange-yellow in colour and 

 rather irregular in shape, ellipsoidal or polyhedral, about 16-22 />, 

 in length and 14-18 /x broad. The spore wall is evenly verru- 

 cose, except a small area, which is smooth, and thinner than the 

 remaining portions. Fig. 6 represents a spore in optical median 

 section, and Fig. 5 in surface view. It will be seen that tlie 

 outer part of the wall consists of a number of rods of material 

 placed perpendicularly to the surface (Fig. 6). Before dehis- 

 cence takes place the spores are found arranged in chains at the 

 base of the pseudoperidium ; when the latter ruptures they easily 

 separate and escape from the opening at the upper end. 



A fungus known as Cccoma Laricis bears a considerable 

 resemblance to t^ e form just described on the larch. Cceotna 

 Lands produces orange-yellow spots on the leaves, but is 

 at once distinguished from Peridermium Laricis by the entire 

 absence of the pseudoperidium, as well as by differences in the 

 sculpturing of the spore wall. Ccwma Laricis has been shown 

 by Klebahn and others to be the aecidial stage of six different 

 species of Melampsora, in which the uredospore and teleutospore 

 stages occur on various species of Populus and Salix. 



Although no definite record of the occurrence of Peridermium 

 Laricis in Great Britain or Ireland has been made [The atten- 

 tion of the authors has been recently called to a paper by Mr 

 W. S. Jones on Melatnpsoridiuin Betulinum {Quart. Journal of 

 Forestry, Vol. V., No. 2, p. 137), where he records the discovery 

 of this disease in Bagley Wood, near Oxford, in 191 1. We 

 rec^ret that, inadvertently, this important paper was overlooked. 

 Dr Somerville informs us that the disease is very common in 

 Ireland.], it is probable that Plowright,^ in 1891, carried out ex- 

 periments with this species. This investigator discovered a form 

 of CcBoma Laricis near King's Lynn, the aecidiospores of which, 

 when placed on Betula alba caused infection, and, in course of 

 time, the uredospore and teleutospore stages of Melampsora 

 hetulina were produced. A subsequent infection oi Larix eurof>cea 

 by the germinating teleutospores produced spermogonia only. 



^ Einige Impfversuche init Kostpilzeu, Zeitschr. f. Pflanzenkr., Bd. i. 

 1891, p. 130. 



