PLANT HORMONES 



157 



nature of the growth process. Although 

 only a few tentative steps towards a better 

 understanding of growth and development 

 could be made, still the evidence in favor 



flower forming 



Fig. 2. Schematic drawing of a plant with root 

 system, stem, old and young leaf and apical bud. 

 Some of the known correlations are drawn with 

 broken arrowed lines, indicating the factors re- 

 sponsible for these correlations. The sugar inter- 

 relations are not shown. 



of a chemical concept has become very 

 strong, and a concrete picture can replace 

 the older stimulus concept. Although we 

 still have a long way to go, the results ob- 

 tained justify confidence in a rapid and 

 fruitful development of our knowledge con- 

 cerning growth and development. Conklin 



in his opening paper stressed the absolute 

 necessity of scientific cooperation, and how 

 every advance has been not so much the 

 discovery of a single individual as a general 

 growth of ideas from generation to genera- 

 tion, a transfer of thoughts between indi- 

 viduals. There are few fields which have 

 so benefitted from interaction between in- 

 dividual scientists, between botanists, phy- 

 siologists, chemists, geneticists, horticultur- 

 ists, and biochemists as the field of plant 

 hormones. If I have mentioned names of 

 individuals in the preceding discussion, 

 their work was worth mentioning, but 

 hundreds of others have helped to build up 

 our present picture. In general, a splendid 

 cooperative spirit exists amongst these 

 plant-hormone workers, a spirit which tran- 

 scends borders and political differentia- 

 tion. 



In the second place, I have tried to view 

 a few of the problems of plant develop- 

 ment from so broad an angle that the es- 

 sential similarity between processes in plant 

 and animal would be stressed. So far 

 botany has learned more from animal phy- 

 siology than the reverse; let us hope that 

 the investigation of the principles of plant 

 growth will be of help to zoologists as well. 

 The greater complexity of an animal makes 

 it more difficult to establish the fundamen- 

 tal basis of its development, and in this 

 respect the investigation of plants has 

 great advantages over that of animals. Be- 

 cause of their differentiation and organiza- 

 tion, the micro-organisms cannot be of the 

 same help to us here as they have been for 

 the investigation of so many fundamental 

 properties of the cell, as van Niel so well 

 pointed out. But in respect to an increase 

 in our knowledge of growth and develop- 

 ment, the plants have the same relation to 

 animals as the micro-organisms have to the 

 higher forms of life. 



In conclusion, I want only to mention 

 that increase in our knowledge concerning 

 the basic principles of plant growth inevi- 

 tably leads, and in fact, has led, towards 

 practical applications in agriculture and 

 horticulture. No better example of the ap- 

 plication of so-called pure research to prac- 

 tical problems could be quoted than this 



