Pflanzenkrankheiten. 43 



working parasite. Two or more years of infection are probably 

 required to produce the death of the tree. 



Apple trees planted on newly cleared land are more liable to 

 attack than those on land cleared and cultivated for some time 

 before planting. 



Three species of Xylaria have been obtained in pure culture 

 from affected apple roots. X hypoxylon obtained from orchards at 

 nine places proved to be an active wound parasite on living apple 

 roots in moist Chambers and in the field. Typical black rootrot 

 Symptoms were produced and recovery in pure culture was obtai- 

 ned. Xylaria sp. (undetermined) from one source also proved patho- 

 genic. X polymorpha from two orchards at one place proved only 

 slightly, if at all, pathogenic. X hypoxylon is probably the chief 

 cause of black rootrot of the apple in Virginia. 



Exclusion practices are suggested as control measures of pro- 

 bable value. M. J. Sirks (Wageningen). 



Long, W. H., A Honeycomb heart-rot ofoaks caused by 

 Stereum stibpüeatum. (Journ. Agric. Research. V. p. 421 — 428. 

 PI. 41. 1915.) 



In addition to the rots produced by Polyporuspüotae, P. berkeleiji, 

 F. frondosus and P. dryophihiSj in the National forests of Arkansas 

 and in other sections of the United States, another type of rot 

 was found in oaks. This undescribed rot is of the pocketed type 

 and is a typical delignifier of the heartwood. In the final stages of 

 this rot the diseased wood resembles a piece of honeycomb. It is 

 caused by Stereum suhpüeatum. 



The writer gives a description of the disease with both macros- 

 copic and microscopic characters and compares this rot with such 

 caused by other fungi. The fungus, so far as the writer knows, 

 enters the wood of the hosts only through wounds which expose 

 the heartwood. At the end of the life history the writer gives a 

 description of the sporophore of Stereum suhpüeatum with notes 

 on its distribution in the United States. 



The only practicable method of control is to prevent, as far as 

 possible, the infection of the trees. This can be done by eliminating, 

 as far as possible, all forest fires, since they produce wounds on 

 the butts of the trees through which the fungus enters and by 

 preventing the formation of the fruiting bodies of the fungus which 

 produce the spores. 



The rot produced by 5. subpüeatum can continue to grow in 

 a tree after it is felled and that every cull butt, log, or tree left on 

 the ground in a lumbering Operation will later bear an enormous 

 number of sporophores. Jongmans. 



Melhus, I. E., Hibernation of Phytophthora infestans i n t h e 

 Irish potato. (Journ. Agric. Research. V. p. 71—102. PI. 4—8. 

 3 Fig. 1915.) 



It is clear from the author's experiments that the mycelium of 

 Phytophthora infestans spreads in the tissues of the potato tuber 

 and finally reaches the sprouts. The growth of the fungus is 

 retarded when diseased tubers are held in dry soil or at tempe- 

 ratures below 5° C. Infected tubers rot rapidly when placed in 

 warm wet soil. This explains the wide Variation in stand obtained 



