559 



which in spring had injured the but Uttle matured branches\ the theory 

 that a discomycetous fungus Dothiora sphaeroides Fr. produced the dying- 

 finally prevailed. In other places a different fungus, Didymosphacria 

 populina, was made responsible for it^. Vuillemin* cites Maminia fimbriata 

 in the dying of the twigs of the hornbean and Didymosporium salicinutn 

 as the destroyer of zvUlotv plantations. Finally we will call attention once 

 more to the dying of the red alders described by Appeh^ as due to Valsa 

 oxystoma, which ftmgus can complete its work of destruction only in speci- 

 mens weakened by disturbances in nutrition. 



Freezing of the Spring Growth. 



If late frosts surprise the tree at a time when the leaf buds have began 

 to elongate, or have already developed into short shoots, repeated injuries 

 and also phenomena of regeneration will then set in. A case which I have 

 found frequently in cherries shows the dying of the youngest growing 

 point in the opening leaf bud. Hie injury is not noticeable at first since all 

 the leaf buds have remained intact. After some time, however, a peculiar 

 spreading appears, called forth by the turning back of the very turgid 

 bracts and the absence of growth excites investigation. Later, sickly, 

 lateral shoots appear from the uninjured lateral buds and at times also a 

 fasciated growth after such spring injuries. 



I succeeded not long ago in producing the same kind of disturbance 

 by the action of artificial frost. Fig. 121 represents a cherry branch in 

 which three buds have lost their growing points from frost. The vegeta- 

 tive activity, very energetic in the spring, has so made itself felt in the two 

 upper buds that the bract-like, early leaves have become larger, a darker 

 green and fleshier and have spread out from one another almost hori- 

 zontally. At the lowest bud there is a beginning of two lateral compen- 

 satory shoots. 



In Fig. 121 B the condition of the bud with a frozen growing point is 

 more exactly reproduced. The growing point (a) is blackened and dried 



1 The explanation of this disease as a result of frost has been substantially sup- 

 ported by the observations of Count von Schwerin (Gartenflora 1905, Part 5, p. 400). 

 He proved, on an Italian trip, that south of the Alps the pyramidal poplars were 

 not diseased, i. e. no degeneration of this tree could be observed in its present home. 

 Its death, occurring in bands throughout Germany, is explained simply as the result 

 of spring frosts repeatedly occurring at the end of the '70's after long, damp and 

 mild autumns. Of the earlier observers Hausknecht (Bot. Ver. f. Gesamtlhiiringen; 

 cit. Bot. Centralbl. 1SS4, p. 275) had already called attention to the fact that the 

 dying showed itself almost entirely in the river valleys and depressions, but spared 

 higher positions. We find another valuable note by Pertsch in St. Petersburg 

 (Deutsche Gartnerzeitung 1884, No. 10). He found on a trip through northern, 

 western and central Germany that the length of the dead tips became constantly 

 shorter, the farther south he went. The fact that Populus pyramidalis is not found 

 in St. Petersburg, while P. alba, P. laurifolia, P. suaveolens, P. Balsamea, etc., thrive 

 there shows that it is more susceptible to frost than most of the poplars. 



-' Rostrup, Pyramidepoplens Undergang. Tillaeg til Nationaltidende 13. Novem- 

 ber 1883. 



■" Vuillemin, P., Remarques etiologiques sur la maladie du Peuplier P5'ramidal. 

 Revue mycol. 1892, p. 22. 



4 Vuillemin, P.. Titres et travaux scientifiques. Paris 1890. 



"■' Appel, O., tJber bestandweises Absterben von Roterlen. Naturwiss. Z. f. 

 Land- u. Forstw. 1904. 



