20 W. J. Robbins 



tuted phenoxy acids, including 2,4-dichlorophenoxyacetic acid (2,4-D), 

 2,4,5-trichlorophenoxyacetic acid (2,4, 5-T), and chloro-substituted ben- 

 zoic acids were some of those first tested in his laboratories. 



However, Percy Zimmerman was not a narrow botanical and hor- 

 ticultural specialist. He served wherever his service would benefit his 

 friends and neighbors and actively participated in a wide variety of 

 community activities (6). 



We have come a long way since Darwin at his country home out- 

 side London satisfied, so far as he was able, his curiosity about the 

 response to light of the coleoptiles of Phalaris and Avena. He had 

 the aid of tinfoil, India ink, flat splinters of glass, thread, and similar 

 pieces of "complex apparatus," but above all, a clear, inquiring, and 

 logical mind, and the serenity of a peaceful household managed by 

 a devoted wife. A long succession of able and dedicated investigators, 

 among whom we include Percy ^V^ Zimmerman, have answered some 

 of the questions Darwin's investigations raised and carried on into 

 areas of which Darwin never dreamed. Not the least of these areas 

 is that of the effects of minute quantities of specific organic com- 

 pounds — call them auxins, vitamins, hormones, growth regulators, or 

 what you will — on the growth and development of plants. Investi- 

 gation of these substances promises to be for some time to come one 

 of the most important fields in plant physiolog). To those who have 

 and are contributing to this subject, we might well say in the Avords 

 of Swinburne: 



Tliy ivorks and mijic are ripples on the sea. 

 Take heart, I say; xve knoiu not their end. 



LITERATURE CITED 



1. Boysen Jensen, P. Uber die Leitung des phototropischen Reizes in Avena- 

 keimpflanzen. Ber. Deutsch. Bot. Ges. 28: 118-120. 1910. 



2. , and Nielsen, N. Studien iiber die hormonalen Beziehungen zwischen 



Spitze und Basis der Avenacoleoptile. Planta. 1: 321-331. 1925. 



3. Branner, L. Lichtkrinnmung und Lichtwachstumsreaktion. Zeitschi. Bot. 14: 

 497-517. 1922. 



4. Darwin, C. The Po^^e^ of M()\cmcnt in Plants. 592 pp. J. Murray, London. 

 1880. 



5. Fitting, H. Die Leitung tropistischer Reize in parallelotropen Pflanzenteilen. 

 Jahrb. Wiss. Bot. 44: 177-253. 1907. 



0. Hitchcock, A. E. Percy W. Zimmerman (February 23, 1884 — August 14, 1958). 

 Contr. Boyce Thompson Inst. 20: 1-5. port. 1959. 



7. Jost, L. Lectures on Plant Pliysiology (transl. R. J. Harvey Gibson). 564 pp. 

 Oxford. 1907. 



8. Loeb, J. Rules and mechanism of inhibition and correlation in the regener- 

 ation of Bryophyllum calycinum. Bot. Gaz. 60: 249-276. 1915. 



9. Miller, C. O., Skoog, F., Saltza, M. H. von, and Strong. F. M. kinetin, a 

 cell division factor from deoxyribonucleic acid. Jour. .\mcr. Chem. Soc. 77: 

 1392. 1955. 



