DANGEROUS INTERNATIONAL FOREST TREE DISEASES 77 



In attacked needles remaining on the shoots are formed apothecia 

 which in spring become easily visible in the shape of 2 to 15 mm. long, 

 narrow, grey-brown to grey-black ribs on the lower side of the needles. 

 The numerous cylindrical asci contain 8 (rarely 4) hyaline, unicellular 

 spores, elongated droplike or obliquely club-shaped, each measuring 

 30-50 X 4-6ju and being surrounded by a slime mantle. Apothecia 

 open in May or June by a longitudinal split. Discharged spores in- 

 fect new needles. Killed old needles, then pale reddish grey to almost 

 white in color, are dropped during summer. 



The infection period in spring is short — infection apparently suc- 

 cessful only in juvenile needles after abundant rain. Attack is often 

 very uneven within the stand, partly owing to variations in time of 

 flushing. Marginal trees and trees in openings are most frequently at- 

 tacked. Though all age classes are susceptible, 10- to 30-year-old indi- 

 viduals are as a rule most easily infected. 



Both plantations and spontaneous forests are attacked. 



Because only the current year's needles are infected, trees are never 

 reported killed. Repeated attack several years in succession causes 

 stunted growth with abnormally short shoots. 



The disease is reported mainly from the temperature zone of 

 Scandinavia, being mentioned also from Scotland and the Pyrenees 

 (and other parts of Spain). In Germany it is probably frequent al- 

 though there it is most often attributed to attack by a pycnidiferous 

 fungus Hendersonia acicola v. Tub. with brown, elongated, ellipsoidi- 

 cal, 3-septated spores. This fungus is often, incorrectly, considered 

 the conidial stage of Hypodermella sulcigena. In Scandinavia Hen- 

 dersonia occurs as a secondary fungus in needles attacked by Hypoder- 

 mella, and its presence seems to depress the apothecial formation of the 

 last-named. 



Hosts: Pinaceae — 

 Pinus sylvestris L. 

 P. mugo Turra 



P. nigra var. austriaca Asch. & Graebn. 

 P. haUpensis Mill. 



(A disease on this species in Spain recently mentioned to me by 

 Dr. J. B. Martinez, seems to be identical with ours.) 

 Intercontinental spread possible through shipment of plants, trees, 

 and cuttings. 



Literature: 



Lagerberg, T. Om grabarrsjukan hos tallen, dess orsak och verknin- 

 gar. "Die Hypodermella-krankheit der kiefer und ihre Bedeu- 

 tung." Meddel. f. Statens Skogsf0rs0ksanst. 7-8, Stockholm 

 1910. 



Rostrup, E. Fortsatte undersgelser over Snyltesvampes Angreb paa 

 Skovtrserne. Tidskr. f. skovbrug, V. 6, Copenhagen 1883. 



Pine Twist Rust 



J. Gkemmen 



Forest Research Station, Wageningen, Netherlands 



Melampsora pmitorqua Rostr. is a heteroecious fungus developing 

 its pycnial (spermogonial) and caeomatal (aecial) stage on Pinus 



