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spite of thèse difficulties, there is not a single one in 

 whicli a scale-insect may be seen in a sucking position. 

 But always in the places were an insect was on the leaf, 

 in the tissue the changes were found which we described 

 as characteristic for the yellow vesicles. 



Hère also hypertrophy, accompanied by disorganisation 

 of the cholorophyl, of cells, belonging to the mesophyl; 

 some of thèse cells hâve brown walls. Also in the epiderm 

 on which the scale-insect is found, some cells are found, 

 the walls of which are suberized and which besides are 

 sometimes slightly swollen. 



I was more fortunate with hand-made préparations, 

 some of which show the suction apparatus of the scale- 

 insect inside the leaf tissue. From thèse we see that in 

 the yellow vesicles those cells, the wall of which has 

 become suberized, hâve been in direct contact with the 

 suction apparatus of the scale-insect and that the other 

 cells, that become hypertrophical, only react to a stimulus, 

 exerted by the wounded cells. On the character of this 

 stimulant action we shall speak presently. 



That hère the enlargement of the cell should take place 

 at the expense of its own contents, as is stated for many 

 similar hypertrophical processes, is not the impression I 

 received. Although in many of the very strongly hyper- 

 trophical cells a large central vacuole may be observed, 

 yet I saw nowhere réduction of the protoplasm to a very 

 thin wall-lining. The nucleus does not show any déviation 

 and the cell-wall does not become perceptibly thinner. 



That the sting of the scale-insect not only causes the 

 formation of the yellow vesicles but through them also 

 ail further changes, including the formation of the adven- 

 titious buds, has become clear to me by: 



1. the microscopical examination of a very large number 

 of préparations, relating to thèse stages; 



2. the continued observation of a number of leaves on 



