Formative Effects of 

 Hormone-Like Growth Regulators 



p. W. ZIMMERMAN 



FORMATIVE effects may be defined as changes in pattern from that 

 normally resulting from the genetic constitution of the plant under 

 the influence of particular environments. When the environment is 

 more or less constant for a usual habitat, the size and shape of the plant 

 and pattern of organs are said to be normal for a given species. Unusual 

 environments involving temperature, moisture, light, or chemical sub- 

 stances bring about different expressions of so-called normal character- 

 istics. The results may be referred to as formative effects brought about 

 by a given combination of influences. At this time we shall be concerned 

 especially with chemical influences. 



There are three groups of chemical compounds which cause modifica- 

 tions in form of plants. These are /?-naphthoxyahphatic acids (13), substi- 

 tuted phenoxyaliphatic acids, and substituted benzoic acids (14). There 

 are other less well-known synthetic compounds and even extracts of 

 plant tissue which have formative influences. In addition to having a 

 formative influence, the naphthoxy and phenoxy groups of compounds 

 have many other hormone-like characteristics. For example, they cause 

 cell elongation, cell division, curvatures, and induction of roots. The 

 derivatives of benzoic acid cause formative effects with little or no cell 

 elongation. 2,3,6-Trichlorobenzoic acid is an exception. 



There is need for a single term to cover all substances which have 

 formative effects on plants. The word formagen was proposed by Zim- 

 merman and Hitchcock (15) and used by King (5). Beal proposed the 

 word telomorphic (2), but neither of these words has been widely 

 accepted. I shall, however, use the word formagen at present as a matter 

 of convenience. 



