( 1.78 ) 



expense of its own contents, as is stated for many similar hypertro- 

 phical processes, is not the impression I received. Although in many 

 of the very "strongly hypertrophical cells a large central vacuole may 

 be observed, yet I saw nowhere reduction of the protoplasm to a 

 very thin wall-lining. The nucleus does not show any deviation 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 all further changes, in- 

 cluding the formation of the adventitious buds, has become clear to 

 me by : 



1. the microscopical examination of a very large number of 

 preparations, relating to these stages ; 



2. the continued observation of a number of leaves on the tree, 

 showing that those leaves on which scale-insects or the yellow 

 vesicles caused by them, were seen, underwent the above described 

 changes, while the control leaves remained free from. them. On 

 Sept. 13, 1906, the top of that plant which forms adventitious buds 

 most strongly and one of its branches were each surrounded by a 

 muslin balloon, after they had first been carefully inspected and 

 cleaned. "^These balloons were supported by skeletons of galvanised 

 iron wire and closed below by pulling them on to a pad of cotton 

 wool, placed round the sprout, At the top of the plant were then 

 only young leaves, on the branch full-grown ones, all of them free 

 from scale-insects and vesicles. The balloon, surrounding the top of 

 the plant had repeatedly to be replaced by a bigger one as the 

 top grew. 



On January 22, 1907, the balloon was removed from the branch ■ 

 and the leaves were examined. Of two of these leaves the extreme 

 part of the top had turned yellow. A microscopical examination of 

 these leaf-tips showed, however, that here was no initial stage of 

 bud-formation. Hypertrophical cells, such as we ought to have found 

 in this case in the mesophyl, were not present. The yellow colour 

 was caused by the dying of the tissue, the cell-contents then dis- 

 colouring. 



On May 10 the top of the plant was liberated. A number of full- 

 grown leaves which at the beginning of the experiment were still 

 young and young leaves at lateral sprouts which during the isolation 

 had been formed by sprouting of the axillary buds, were now seen. 

 All these leaves were perfectly normal, healthy and strong with a 

 normal green colour; on none of them anything could be detected 

 of yellow vesicles or spots, of none the top showed any discolo- 

 ration or thickening. The isolation by means of the muslin balloon 





