( 181 ) 



Woods 1 ) that it is caused l>v the sting of aphides, among others, 

 Woods thinks the growth of the yellow, thickened spots must be 

 ascribed to the diffusion of an irritant, injected by the insect 2 ). 



That a similar hypothesis is superfluous for the "stigmonose" of 

 Gnetum Gnemon, appears clearly enough from our experiments. The 

 specific 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 distinguished in the yellow vesicles by brown walls, 

 have undergone the direct consequences of it, while the whole 

 subsequent formation of the intumescences takes place as a reaction 

 on the stimulating action, proceeding from these few wounded cells. 



Kuster 3 ) calls all cataplasms after vulneration, as far as they have 

 a parenehymatical character, callus. According to this terminology 

 also the tissue of which the thickened leaf-tips of Gnetum Gnemon 

 consist, is a "callus" and the buds, funned in them, are callus-buds 4 ). 



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 fulfilled by the 

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

 temperature in this latter could not but favour the formation of 

 callus with these tropical plants. 



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

 and buds, may be explained in the following manner. 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. 

 And this condition is normally only fulfilled in the tip of the leaf, 

 in another part of the blade only when the organic relation with 

 the tip has been disturbed. 



Botanical laboratory at Utrecht. 



') A. F. Woods, Stigmonose : a disease of carnations and other pinks. (Bull, 

 no. 19. U. S. Dept. Agr. Div. Veg. Phys. and Path. 1900). 



2 ) 1. c. p. 24. 



3 ) E. Küster, Pathologische Pflanzenanatomie. Jena. 1903. p. 154. 



4 ) See also: E. Küster, Histologische und experimentelle Untersuchungen iiher 

 Intumescenzen. (Flora oder allgem. bot. Zeitg. 96 Bd. 1906, p. 527—537). 



