246 



THE PROTECTION OF WOODLANDS. 



Fig. 63. 



laricis, the Birch-rust fungus producing resting-spores in orange-red, then 

 brown pustules, and forming reddish- orange cecidia on Larch leaves. 



In the genus Coleosporium the resting-spores are produced in yellowish 

 pustules on coryinbiferous plants, and especially on Groundsel and Rag- 

 worts (Senecio), and the intermediate 

 stage is called Peridermium, from the 

 bladder-like spore-pustules produced on 

 the leaves of Pines attacked. The com- 

 monest kind is C. senecionis on groundsel 

 and ragwort leaves + P. oblongisporium 

 (formerly called P. pini acicola) on the 

 old foliage of 3- to 10-year-old Pines 

 (and up to 30 years), but never on new 

 leaves. In April and May small orange- 

 yellow blisters appear on the leaves of 1- 

 and 2-year-old shoots, which turn brown, 

 burst, and scatter their spores, while the 

 mycelium hibernates in the leaf and 

 again produces cecidia in the following 

 year, the leaves killed showing small, 

 blackish, warty spots with light edging. 

 The only means of prevention is to dig 

 up and burn all ragwort and similar 

 corymbiferous plants in the immediate 

 neighbourhood, and to cut and burn 

 infected Pine twigs. 



* In the genus Cronartium the inter- 

 mediate stage is also called Peridermium, 

 as the spores are here again produced in 

 bladders ; and to it belongs the several 

 blisters or bladder-rusts on the stems of 

 Pines (formerly called P. pini corticola). 

 The chief disease of this genus is the 

 Pine bark-blister (Fig. 63), a Cronartium 

 species + Peridermium pini, the resting- 

 spores of which are produced in rusts on 

 foliage of peonies, Ribes, and Cynanchum, 

 and the peridermium-st&ge passed on the 



stems of young Pines, and especially on poor soil with a S. or S.W. exposure, 

 where it may become epidemic and do serious damage. It is purely a wound- 

 parasite, and mainly attacks Pine-poles 15 to 20 years old, and thick-barked 

 parts over 25 years seem immune. It mostly appears first at whorls 

 near the top of the crown, and as the oval pustules filled with reddish- 

 yellow spores break out as blisters on the bark of stem and branches in 



Pine-shoot with sporophores of 

 Peridermium pini. 



a. Blisters that have not yet dis- 



charged their spores. 



b. Ruptured blisters from which 



the spores have been partly 

 scattered. 



