169 



our experiments. The spécifie point about the wound, made 

 by the suction organ of the scale-insect Is only that it Is so 

 trifling. Only a few cells, namely those which are distin- 

 guished in the yellow vesicles by brown walls, hâve under- 

 gone the direct conséquences of it, whlle the whole subsé- 

 quent formation of the intumescences takes place as a 

 reaction on the stimulating action, proceeding from thèse 

 few wounded cells. 



Kùster ') calls ail cataplasms after vulneration, as 

 far as they hâve a parenchymatical character, callus. Accor- 

 ding to this terminology also the tissue of which the 

 thickened leaf-tips of Gnetum Gnemon consist, is a „callus" 

 and the buds, formed in them, are callus-buds ^). 



Why the two plants from the cooler hothouse did not 

 form callus or buds on their leaves, is now also clear. 

 The Aspidiotus, playing such an important part in this 

 formation of callus, is also found in the cooler hothouse; 

 but for callus-formation the chief condition is humidity. 

 This condition was only to some extent fulfiUed by the 

 cooler, but completely by the hotter house, while also the 

 higher température in this latter could not but favour the 

 formation of callus with thèse tropical plants. 



Why only the apical part of a leaf is capable of forming 

 callus and buds, may be explained in the following man- 

 ner. The small wound causes an afflux of nutrient matter 

 in an apical direction. If now an accumulation of this 

 matter, which is necessary for the hyperplastic formation 

 of callus, shall be possible, the afflux must not be able to 

 pass by, i.e. it must be stopped apically of the wound. 



1) E. K û s t e r, Pathologische Pflanzenanatomie. Jena. 1903 pag. 154. 



2) See also: E. Kûster, Histologische und experimentelle Unter- 

 suchungen ûber Intumescenzen. (Flora oder allgem. bot. Zeitg. 96 

 Bd. 1906, pag. 527—537). 



