406 Scientific Proceedings, Royal Dublin Society. 



grew well, and he maintained the petioles growing for four years. Beyond 

 saying that the petiole liad enlarged to a firm stalk 1-5 cms. in diameter, no 

 details are given. 



V6chting(3) grafted a sprout of the beetroot on a petiole. He gives no 

 further details. 



More recently — 1909 — Kny (4) records some results with Begonia rex. 

 He did not use the grafting method. It is well known that adventitious buds 

 grow readily on the leaves of this plant. The leaf was rooted, and an 

 adventitious bud at tlie base of the lamina was allowed to develop. At the 

 conclusion of the experiment the petiole carried a fine plant. He found in 

 this petiole by comparison with petioles from normal plants that the area of 

 the vascular bundles had greatly increased, and that the old cambium had 

 re-awakened and had become active. The cells of the neighbouring ground- 

 tissue were also in a state of division. 



"Es machte ganz den Eindruck dass liiermit der Beginn der Anlegung 

 eines interfaseikularen Kambiums gegeben war, das bei weiterer ungestorter 

 Fortbildung die peripherischen Biindel zu einemKreisezusammengeschlossen 

 haben wiirde." But lie gives us no more information or discussion. 



In 1907 Winkler (5) published an account of his work on the same 

 problem. He made use of the existence of adventitious buds on the leaves of 

 Torenia asiatica. Tliough with some difficulty, tliey were induced to grow 

 just as Kuy's buds on Begonia rex grew, and considerable secondary tissue 

 developed in the petiole. Normally a simple bow-shaped bundle, an abnormul 

 cambium appeared in the ground-tissue opposite the bundle, and formed with 

 the original a comjplete cambium ring, and eventually a thick cylinder of 

 wood. He gives a very careful description of the origins of the cambium, 

 and ends with an extensive criticism of the possible causes of the secondary 

 wood. His paper will be frequently alluded to in the following pages. 



Finally, we have a short paper by Lohr(6) in 1909. He rooted leaves of 

 many plants — including Pelargonium zonale — and grafted sprouts on them. 

 He gives comparatively few anatomical details of secondary increase in the 

 petioles. 



So much for the historical account. It shows us that the petiole can 

 function as a stem with remarkable changes of structure. But when we com- 

 pare the masterly paper of Professor Hans Winkler with the other contribu- 

 tions, we see at once that his is the most important one. He has realized the 

 importance of the answer to the further query : Whence these changes ? 

 That answer he has himself attempted, but more and more extended and 

 detailed work is necessary to verify that answer. Hence these experiments, 

 which were begun at his suggestion. The first hall of the work was carried 



