490 RADIATION BIOLOGY 



Bissonnette (1932b) and Burger (1943), working with the starhng, 

 Sturnus vulgaris, found red radiation to be most effective in stimulating 

 sexual activity, with green less active and blue ineffective when used to 

 extend a normal light period during winter. Similar results were obtained 

 with turkey, Meleagris gallopavo, by Scott and Payne (1937) and with the 

 sparrow, Passer domesticus, by Ringoen (1942). 



Oestrus in the female ferret was found by Marshall and Bowden (1934) 

 to be uninfluenced by radiation beyond 7500 A. Marked response was 

 obtained throughout the visible spectrum at sufficiently high intensity. 

 Barbanti (1932), working with the field mouse, Microtus agrestis, found 

 that red and yellow radiation stimulated sexual activity. 



Lengthening of certain internodes of various plants is inhibited by 

 fight. In this way the length of underground parts of most seedlings is 

 regulated by light reaching the plants as they emerge. A single low- 

 intensity irradiation for a short period can greatly afTect the development 

 of dark-grown seedfings. This, of course, is not a periodic phenomenon. 

 Abnormalities that occur when plant growth takes place in darkness 

 or at low light intensities are often grouped under the general term 

 "etiolation." There is an extensive literature on etiolation, of which 

 only one aspect, namely, elongation of certain organs of dark-grown 

 seedlings, is considered. 



An action spectrum for one type of etiolation, namely, that for leaf 

 size of dark-grown pea, Pisum sativum, seedlings, has been obtained 

 (Parker et al, 1949). The results are shown in Fig. 10-2. Although 

 these lack precision in the region of minimum effectiveness near 4600 A, 

 nevertheless they are closely related to the action spectra for control of 

 flowering. Similar results were obtained for suppression of elongation 

 in the second internode of barley, Hordeum vulgare (Borthwick et al., 

 1951). Albino and potentially green plants of barley reacted alike. 

 Again it is to be noted that the two action spectra dealing with elonga- 

 tion are eciuivalent even though the one enhances and the other inhibits 

 lengthening of particular structures. 



Goodwin and Owens (1948, 1951), using filters with mercury and 

 sodium arcs, also found the red portion of the spectrum to be most effec- 

 tive for internode inhibition of oats, Avena saliva var. Victory. They 

 measured the variation of response with energy incident on the complete 

 seedling and determined the relative energies at various wave lengths 

 required for a given inhibition of dark-grown seedlings. The action 

 spectra closely follow those of Fig. 10-2, but some minor variations were 

 interpreted as evidence of fine structure. These more likely arise from 

 biological variation, as can be seen by inspection of Goodwin and Owens's 

 curves showing variation of response with energy, particularly the curve 

 for 5890 A. 



