PHOTOPERIODISM 503 



on the treated plants as on the controls. With C. officinalis more nodes 

 were formed below the inflorescence oji the main stem of the treated 

 plants than on that of the controls. 



Floral initiation of the short-night plants Silene armeria and annual 

 Hyoscyamus niger were found by Liverman (1952) to be promoted by 

 auxins applied to plants that were held on photoperiods near the thresh- 

 old for response. Silene plants sprayed with indoleacetic acid solutions 

 elongated much sooner than untreated controls, and there appeared to 

 be a relation between the amount of supplementary light and responsive- 

 ness to applied auxin. 



Control of the length of the first internode of barley is effected by light 

 of the same cjuality as that for control of floral induction. Mer (1951) 

 found that growth of the mesocotyl of Avena saliva did not depend on 

 the auxin diffusing from the coleoptile tip. The length of this structure 

 is strongly controlled by light, and perception is not affected by the 

 action of cyanide or iodoacetate or by anaerobic conditions. The effects 

 of illumination survive a period of drying and become apparent upon 

 subsequent germination of the grain in darkness. Apparently this effect 

 is on the embryo, since perception occurs in embryos excised from dry 

 grain and grown on culture medium. Mer concluded that auxin itself 

 was not the primary reactant in the perception process. 



General observations on the effects of growth-regulating compounds 

 has been determined for different plants by several investigators (Bonner, 

 1940; Clark and Kerns, 1942; Cooper, 1942; Leopold and Thimann, 1949; 

 Van Overbeek, 1946). Clark and Kerns (1942), working with the pine- 

 apple, Ananas comosus, reported that a-naphthaleneacetic acid applied 

 as a foliage spray in concentrations of 0.1 mg/liter hastened floral initi- 

 ation, whereas tenfold higher concentration delayed the process. They 

 pointed out that, even though this compound affects floral initiation, it is 

 not to be considered as a "florigen" but is to be classed with acetylene 

 and ethylene, which also induce premature flowering in Ananas. 



Cooper (1942), working with the Abachi variety of pineapple in Florida, 

 reported that treatment with a-naphthaleneacetic acid in October induced 

 premature flowering, whereas treatments made in July had no effect. 

 Ethylene, however, induced premature flowering equally well in summer 

 and fall. In these experiments separate lots of plants were sprayed with 

 a-naphthaleneacetic acid, a-naphthalene acetamide, and ^S-indoleacetic 

 acid in concentrations of 0.01, 0.005, and 0.001 per cent. Cooper's 

 results with 0.01 per cent a-naphthaleneacetic acid differed considerably 

 from those of Clark and Kerns (1942) in Hawaii in that the treatment 

 hastening flowering in Florida delayed flowering in Hawaii. 



Van Overbeek (1945, 1946) worked extensively with pineapple in 

 Puerto Rico. He observed that solutions of a-naphthaleneacetic acid or 

 2,4-dichlorophenoxyacetic acid applied to the crowns of vegetative plants 



