I 



1917] CURRENT LITERATURE 241 



r 



fig. 8). It appears not improbable that these may be accidental depressions, 

 for in many cases of actual penetration figured such indentations are not 

 evident. 



In the study of the action on the cuticle of extracts and exudates of germ 

 tubes, Brown found that when the extract of germ tubes was placed in con- 

 siderable quantity on intact leaves and petals of Viola, Petunia, Dahlia, Vicia 

 Faba, and Begonia her aclae folia, no effect was produced; but in experiments 

 with Tropaeolum, Geranium, Rosa, and Fuchsia a varying number of discolored 

 spots appeared on the surfaces covered by the drops. The action in these 

 cases was attributed to possible wounds in the cuticle. All the extracts were 

 tested also on wounded leaves and petals, and in those cases in which no action 

 was observed, the corresponding experiments on uninjured leaves and petals 



were rejected. Thus conclusions were drawn only from extracts known to be 

 active. 



When spores were sown in drops of liquid on the surface of leaves, the dis- 

 coloration appeared first around the margin of the drops where the spores 

 germinated earliest. When such drops, containing germinating spores, were 

 displaced slightly on the leaf, the discoloration due to the action of the spores 

 appeared within the area originally outlined by the drop and none in the new 

 area occupied. Infection drops cleared of spores had no action on the most 

 sensitive petals. 



With reference to the possibility of the production of oxalic acid in suffi- 

 cient quantity to cause the death of tissues under the uninjured cuticle, Brown 

 found that solutions of n/40 oxalic acid and of n/20 potassium oxalate placed 

 on the leaves had no effect within a period of 1 2 hours, the time required for the 

 germinating spores to produce discoloration. The maximum concentration 

 in the infection drops, it was shown, could not exceed n/800. 



These experiments seem to show quite clearly that cuticle-dissolving sub- 

 stances are not present in the extracts made from germ tubes of Botrytis 

 cinerea, and that such substances, if they exist, do not diffuse into the surround- 

 ing medium to any considerable extent. The conclusion that chemical action 

 is entirely excluded seems somewhat too sweeping, however, for there still 

 remains the possibility of such action at the point of contact of the germ tube 

 with the cuticle by substances which cannot be obtained in extracts in an active 

 state. The possibility that oxalic acid occurs in sufficient quantities to injure 

 cells through the cuticle seems to be definitely excluded. 



The observation that the germ tubes of Botrytis cinerea exude no substances 

 which are capable of diffusing through the cuticle and killing the cells below 

 corroborates the histological study of Blackmax and Welsfokd, according to 

 which the cells underlying the cuticle are not injured before the cuticle has 

 been perforated. In this respect, the behavior of Botrytis cinerea differs from 

 that of Sclerotica Libertiana, in which DeBary observed a killing of the host 

 cells before penetration of the cuticle.— H. Hasselbrixg. 



