1 86 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



The points of distinction are given below : — 



D. Willkoinmii. Asci subcylindrical, 120 - 140 x 10- 12 /x; 

 ascospores oval, 18-25x6-8//; paraphyses slightly 

 longer than the asci. 



D. subtilissiina. Asci narrowly cylindric-clavate, 65 - 70 x 

 7-8 //; ascospores slightly curved, 8-10x2 \i; 

 paraphyses equal in length to the asci. 



The asci and spores of the two species are shown in Plate XIX. 

 Figs. 4 (D. siibtilissuna) and 5 (Z). Willkommii), which are 

 drawn at the same magnification. 



The conidial fructifications of D. Willkonimii have been often 

 described, but it appears that up to the present no account of 

 those of D. subtilissima has appeared. The pillar-like conidial 

 fructifications of the latter species are smaller than the 

 ascophores, being about i mm. in height (Fig. 3, b). The 

 lower portion is white, and this is surmounted by a head of a dark 

 yellow colour. The fructification is in reality in the form of a 

 stalked irregularly shaped cup, which is completely filled up with 

 a yellow mass of minute ellipsoidal conidia, measuring 3 x i /x 

 (Fig. 6). The interior of the cup is entirely covered with a layer 

 of minute branched conidiophores which bud off the hyaline 

 conidia from their apices (Fig. 7). 



D. subtilissima has been recorded by Massee on Abies 

 pectinata and Larix europaa. A specimen on larch received 

 by Greville in 1822 from Sir A. Jardine of Jardine Hall, 

 Dumfries, and identified by Cooke, is preserved in the 

 herbarium of the Royal Botanic Garden, Edinburgh. While 

 writing this account, specimens on Finns Thunbergii and 

 Finns densiflora have been received from Dunkeld from 

 Mr J. Murray, and on these the fungus has produced 

 cankers of the usual kind. 



The occurrence of D. subtilissima on several host species 

 is of considerable importance, since it is probable that the 

 fungus can pass from one species to another. Experiments 

 are being carried out to determine whether the larch can 

 be infected by the fungus from the Scots pine, and if these 

 are successful the possibility of such infection may lead to a 

 modification in our views on the occurrence and distribution 

 of the larch disease. 



