55^ 



branch r)nl}- when it has liLconic diseased, or at least weakened, as a resuU 

 of disturbances in nutrition due to atmospheric or soil conditions. On 

 such a foundation no further injury is needed for the penetration of the 

 fungi ; this can take place also through the lenticels. The disturbance in 

 nutrition, which must of necessity exist previous to the infesting by such 

 parasites of weakness, is not always necessarily caused by frost. Unsuitable 

 habitat and excess of moisture or drought, etc., can just as well give tiie 

 first impetus. Ldstner considered the last named factor as the cause of 

 weakening in the cherr}- trees on the Rhine, while I would rather hold to 

 the theory that, in the majority of cases, injuries due to frost, and in fact 

 those which take place in spring, represent the [)rimary cause. 



Accordingly. I see only a very slight consolation in the careful destruc- 

 tion of the parts attacked by fungus. One should not forget esjjecially 

 the ubi(|uity of the Cytosporeae and similar groups f)f fungi. The main 

 point is the cuUiiHitlon of varieties ■z^'hleh Inrve adjnsled fheiiiseiz'es to a 

 definite lueallty. llesides this one should exi)eriment to see whether the 

 sensitiveness to frost can be decreased by an addition of calcium to soils 

 rich in humus. 



r.KAN(.H Ib.lCIir IN T-'oKI'-ST TkEKS. 



1 judge in the same way, as in the d\ing of the cherry tree, a disease 

 which l'\ickel has observed in apricots and peaches. A characteristic yel- 

 lowing and wilting of the ff)liagc with a sul)sc(|uent dying of scattered 

 branches began in June. T'\ickel considers Cytospura nibeseens as the cause 

 and J 'also pntiiasfrl Vr. as the perfect stage. 



()f the better known occurrences of diseases of this character. I will 

 add here "the black blight of red beech shoots." According to W'illkomm' 

 the cause of the dying of the shoots, which turned black at the base, should 

 be sought in a fungus which develoi)s a conidia form like I'ttslsporiiiiii 

 candlciiin Lk. and ma}' be associated with Llbertella fcu/lnea Desm. 'J'he 

 perfect stage would accordingly be Qitafernarla Perscoonli Tul.- 



The dying of the pyramidal poplars which was found in varying inten- 

 sity through northern and central Germany aroused discussion at the begin- 

 ning of the 8o's in the last century. A similar occurrence had been 

 observed in luigland between i(S2o and 1840''. Younger shoots had brown 

 places in the bark under which the wood body also was usually attacked. 

 The lea\ es became yellowish and limp and the branch died. 



Among the different theories which were brought forward to explain 

 the phenomenon, the degeneration of the species through continued sexual 

 propagation jilayed a chief role. Although much reference was made, from 

 the beginning, to the fact that a late frost might be taken as the cause, 



1 Wlllkomm, Die mikro.skoiii.schen Feindo dos \V;ildes, ISGU, I'urt 1, p. 101 



- Selccta t'ung'. carp. II, p. 105. 



■■■ Biolog. Centralbl. XI, 1891, p. 129. 



