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the tree, showing that those leaves on which scale-insects 

 or the yellow vesicles, caused by them, were seen, under- 

 went the above described changes, while the control leaves 

 remained free from them. On Sept. 13, 1906, the top of 

 that plant whlch 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. Thèse 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, ail 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 thèse 

 leaves the extrême part of the top had turned yellow. A 

 microscopical examination of thèse leaf-tips showed, however, 

 that hère was no initial stage of bud-formation. Hypertro- 

 phical cells, such as we ought to hâve found in this case 

 in the mesophyl, were not présent. The yellow colour 

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

 then discolouring. 



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

 of full-grown leaves which at the beginning of the expe- 

 riment were still young and young leaves at latéral sprouts 

 which during the isolation had been formed by sprouting 

 of the axillary buds, were now seen. Ail thèse leaves were 

 perfectly normal, healthy and strong with a normal green 

 colour; on no one of them anything could be detected 

 of yellow vesicles or spots, of no one the top showed any 

 discoloration or thickening. The isolation by means of the 

 muslin balloon had not hindered thèse leaves at ail in their 

 normal development. Only scale-insects and other animais 



