DEVELOPMENT OF THE HORMONE CONCEPT 17 



phenomenon, and Blaauw that they were a growth phe- 

 nomenon. The vertical hne beginning with Paal is intended 

 to be symmetrically placed between the three lines of correla- 

 tion, tropisms, and growth. It goes without saying that 

 such a chart is to a considerable extent arbitrary in its 

 selection, and large numbers of valuable studies are of 

 necessity omitted for one reason or another. An important 

 point brought out by the chart is the true internationalism 

 of these researches, the 27 investigators listed belonging to 

 10 nationalities. 



E. Other Hormones in Higher Plants 



The first investigator actually to work with hormones 

 and active extracts in plants was Fitting (1909, 1910). He 

 also was the first to introduce the word hormone into plant 

 physiology, considering hormones merely as stimulative 

 substances, without stressing the importance of their trans- 

 port. He was able to show that the sweUing of the ovary, 

 and other phenomena of post-floration in tropical orchids, 

 are due to an active substance which could be extracted 

 from the pollinia. 



As mentioned above, Laibach was able to identify this sub- 

 stance (with a high degree of probability) with auxin. 

 An effect of perhaps similar nature has been shown by 

 Swingle (1928) to be exerted in the development of the date 

 fruit by the embryo ("meta-xenia"). Evidence for other 

 types of hormones was obtained by Haberlandt and his pu- 

 pils in a series of investigations, principally on cell division. 

 Their fundamental experiment was the demonstration 

 (Haberlandt, 1913) that in small pieces of the parenchyma- 

 tous tissue of the potato tuber, cell division only occurs in 

 the presence of a fragment of a vein containing phloem 

 tissue. This influence was also shown to be exerted on the 

 parenchjTna if the phloem was separated from it by a thin 

 film of agar. In addition Haberlandt was able to show that 

 cell division is promoted by the presence of crushed cells 

 (1914). 



