\'0L. 43 T O R R E Y A December 1943 



The Formative Influences and Comparative Effectiveness of Various 

 Plant Hormone-like Compounds* 



P. W. ZiMMERMAX 



Plant physiolog}' has gone a long way since Boysen- Jensen discovered that 

 the stimulus which causes cell elongation and tropic curvatures in coleoptiles 

 passed through a discontinuity of tissue and appeared to be of a chemical nature 

 ( 1 j . Since that time many chemical compounds, natural and synthetic, have 

 been found which when applied to plants act like hormones. In addition to cell 

 elongation these substances cause cell division, induce new organs, prevent 

 abscission, inhibit buds, modify the pattern of organs, and otherwise regulate 

 the gro^^1;h of plants. Such substances have been given various names as hor- 

 mones, auxins, growth substances, growth promoters, growth regulators, etc. 

 Xone of these designations is satisfactory because a single substance has the 

 capacity to induce several varied responses. The word "fonnative" has often 

 been used to describe the effects of hormone-like compounds on plants. This 

 term did not seem significant until recently when it was found that some of 

 these physiologically-active compounds have a decidedly regulating and "form- 

 ative"' effect on the new growths of the entire plant (5, 7. 3, 4). This is in con- 

 trast with locally induced cell elongation. The subject of this paper concerns 

 especially formative influences and comparative activity of several hormone- 

 like compounds which modify the pattern of leaves, flowers, and fruit and 

 which change the correlation phenomena of organs. 



METHODS AXD MATERIAL 



The activity of growth substances was usually detected by curA-atures re- 

 sulting from induced cell elongation or by formative effects on later growth. 

 The former response occurred within a comparatively short period of time 

 (20 to 60 minutes). Formative effects appeared in days or weeks after the 

 plant had time to produce new organs. The first evidence of formative effects 

 appeared on new leaves which were modified in size, shape, pattern, and tex- 

 ture. Later the effects appeared on flowers, fruit, growth habit, and correlation 

 phenomena of organs. 



The chemicals were applied to plants in water solution, as lanolin prepara- 

 tions, and as vapors. A'arious spreaders were used with water solutions but were 

 generally considered not essential. Water solutions (10 to 300 mg./l.) were 

 sprayed on the plants with a nasal atomizer, applied to the soil, and injected 

 into the stem with a glass capillar}- tube. Lanolin (or other oily substance) 



* Read at the 75th Anniversary Celebration of the Torrey Botanical Club at the Boyce 

 Thompson Institute for Plant Research, Inc. Wednesday, June 24, 1942. 



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