410 Scientific Proceedings^ Royal Duhlin Society. 



to as B, 0, D, as we shall subsequently see. This was for identification 

 when the petioles had been removed for section-cutting. The number 13125 

 shows that it was the 125th plant grafted during 1913. Then follows the 

 date and month. The Egyptian-like hieroglyphic shows how the slit had 

 been made in the petiole — horizontally, vertically, or obliquely. 



Once the initial stages were past, the grafted sprouts grew well. A large 

 number of grafts had been made, so that some were sacrificed at regular 

 intervals, i.e., when 2, 6, 8, etc., leaves had become expanded. In this way 

 the changes taking place in the petiole could be consecutively followed. 



Controls. — The following controls were set up : — 



1. That portion of tlie petiole still attached to the lamina, when that was 

 removed just before the grafting operation, was in every case examined — in 

 many cases in paraffin section, in tlie others in hand section. As well many 

 petioles of many other individuals of Pelargonium zonale v. meteor were 

 examined. In all at least 50 petioles from as many different plants were 

 tested. In this way variations from the normal petiole structure could be 

 noted. In passing it may be remarked that these variations were singularly 

 few. 



2. Leaves were grafted on the main stem of the plant. All the other 

 leaves and buds were removed from tlie plant, and kept removed. These 

 leaves grafted just as well as the sprouts on the petioles. These grafts were 

 referred to as B for identification purposes. 



3. Some plants were entirely debudded, and all the leaves removed except 

 a single one. These leaves grew long and well. They were called D. 



4. Many attempts were made to root single leaves removed from the 

 plant. The conditions for successful rooting were difficult to determine, but 

 still some were successfully rooted. 



Thus we can study the structure of the leaf petiole under these 

 conditions: — 



1. Normally growing with all the ordinary correlational influences of the 

 mother-plant being exercised on it. 



2. With the correlational influence of the growing apices of tlie mother- 

 plant removed. In D we have this state exactly ; in B we have it free from 

 these influences, but with the' wounding stimulus of the grafting acting on it. 

 In both we have it still in intimate connexion with the mother-plant. 



3. With all the influences of the plant removed — in the leaf-cuttings. 



4. With the correlational influences of the growing points of the motlier- 

 plants removed, but subject to the influence of the abnormal sprout growing 

 on itself. 



