Abstract
Equipment has been developed for ultraviolet illumination of sharply bounded test areas of the growing zone of sporangiophores of Phycomyces. The growing zone is opaque for this light and the tropic responses are negative. Periodic short narrow stimuli on alternating sides produce periodic tropic responses when applied at x > 0.5 mm, but none for x < 0.5 mm, where x is the distance below the sporangium. Sustained tropic stimuli, applied at constant x, produce tropic responses for any x > 0.1 mm. The lag between stimulus and response is 3.3 min. for any x > 0.5 mm. For smaller x the lag increases progressively. In all cases the tropic bend occurs at values of x > 0.5 mm. Sustained tropic stimuli, applied at constant height relative to ground, produce relatively sharp tropic bends. The center of the bend is at all times close to the simultaneous position of the stimulated area. The boundaries of a light-adapted zone move less than 0.1 mm in 10 min. relative to the sporangium. It is concluded that the receiving and adapting structures do not move relative to the sporangium, and that the responding system does not move relative to ground. The two systems move relative to each other with the speed of growth. The responding system does not extend above x = 0.5 mm.
Full Text
The Full Text of this article is available as a PDF (692.1 KB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- CASTLE E. S. Growth distribution in the light-growth response of Phycomyces. J Gen Physiol. 1959 Mar 20;42(4):697–702. doi: 10.1085/jgp.42.4.697. [DOI] [PMC free article] [PubMed] [Google Scholar]
- CURRY G. M., GRUEN H. E. Negative phototropism of Phycomyces in the ultraviolet. Nature. 1957 May 18;179(4568):1028–1029. doi: 10.1038/1791028a0. [DOI] [PubMed] [Google Scholar]