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Luminescence phenomena have been known for perhaps as long as man has been recording history, but it has been only recently that some of these phenomena have been utilized in the study of plant tissues. Anything which can disturb the energy equilibrium within an atom of matter is at least intrinsically capable of causing that atom to emit light. As a corollary to this, any form of matter capable of absorbing energy is potentially capable of being excited to luminescence. Many biological compounds are in this category and most of them emit visible light when irradiated by invisible ultra-violet light. If the luminescence ceases when the incident radiation is removed, the term flourescence, which was first used by Stokes in 1852, should be used to describe the condition. On the other hand, if the luminescence persists for a time after the exciting radiation has been stopped, the term phosphorescence is proper. Since color is at best a qualitative measure of light, either the frequency or wavelength must be considered in any study employing monochromatic light. Many of the early workers have neglected this point, consequently their work is often difficult or impossible to duplicate. A wavelength of 365 millimicrons has been employed in the current study. This wavelength is slightly shorter than the barely visible violet part of the spectrum. The average human eye is sensitive to wavelengths between 400 and 700 millimicrons, and since the ultra-violet range is located between the shortest visible light rays and the longest X-rays, that part of it which is near (in wavelength) to the visible is called the near ultra-violet. Biological materials fluoresce most strongly in this region and the researches of many have shown that maximum fluorescence occurs when the exciting radiation has a wavelength of approximately 365 millimicrons. This method has been little explored in the study of plant anatomy. Based upon the hypothesis that changes incident to maturation should also produce a change in the fluorescence of plant tissues, this paper represents an attempt to discover and describe some of these changes.

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Proceedings of the Iowa Academy of Science





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©1956 Iowa Academy of Science, Inc.



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