PRELIMINARY OBSERVATIONS ON GROWTH AND 

 PHOTOTROPIC RESPONSE OF OAT SEEDLINGS 



By ENOCH KARRER 



Division of Radiation and Organ-isms, Smithsonian Institution 



If oat seedlings are germinated while exposed to the continuous 

 spectrum, the shoots in the blue region will curve toward the light 

 source. This bending out of the plane of the spectrum is the ordinary 

 phototropic response. In addition there appears to be a bending within 

 the plane of the spectrum. The curvature in the blue just mentioned 

 has components in the plane of the spectrum such that the tips of 

 the seedlings converge. In the deep red, seedlings do not converge as 

 in the blue, but diverge in the plane of the spectrum. In this region 

 there is no bending out of the plane of the spectrum. There is no 

 ordinary phototropic sensitivity (i)^ in this region. 



The components of curvature in the spectral plane seem not to be 

 an effect of intensity gradient, but rather of a wave-length gradient, 

 for the convergence and divergence occur on both sides of a particu- 

 lar narrow spectral region. It might also be the effect of a concentra- 

 tion gradient of a substance emanating from the seedlings. Such 

 substances must themselves be products resulting from the effects of 

 the radiation. The convergence occurs in the region of wave length 

 4.750. The divergence occurs in the region of wave length about 6,220. 



As for other types of spectral response : the greatest elongational 

 growth was in this blue region of convergence, and the next greatest 

 in this red region of divergence. The greenest growth was in the 

 region from 5,910 to 6,130; the yellowest from 4,356 to 5,200. Roots 

 were longest in the extreme blue (4,356-4,800), and shortest beyond 

 6,200. The leaf sheath (the coleoptile) was most filled out by the first 

 leaf in the green and orange ; least filled out in the blue and deepest 

 red regions. In the green region there appeared to be stunted growth 

 of the coleoptile and the inner leaf broke through prematurely, but 

 later growth in white light of seedling taken from this region was 

 rapid. In the green, and at certain places toward the red, there ap- 

 peared to be evidence of negative phototropy involving only the ex- 

 treme tip of the coleoptile. 



The spectrum utilized was obtained from a concave grating. The 

 wave-length intervals throughout the spectrum are uniform. The 



^ Numbers in parentheses refer to list of literature cited at end of paper. 

 Smithsonian Miscellaneous Collections, Vol. 95, No. 9 



