XXVI 



THE EFFECT OF ULTRA-VIOLET RADIATION UPON SEED 



PLANTS 



H. W. Popp AND F. Brown 



Department of Botany, The Pennsylvania State College, State College, Pa. 



Introduction. The effect upon seed germination and early growth of seedlings: Earlier 

 investigations — More recent investigations — Summary. General studies on the effect 

 upon more mature plants: Introduction — Injurious effects of short-wave ultra-violet 

 radiation — Plants grown in daylight from which the ultra-violet portion was removed. 

 Plants grown in daylight with additional short daily irradiation from a mercury-vapor 

 lamp — Plants grown exclusively under artificial illumination — Plants grown under 

 special ultra-violet transmitting glasses — General s%immary. Other relations to seed 

 plants: Introduction — Absorption and reflection of ultra-violet radiation by plant tissues — 

 Ultra-violet radiation and fluorescence of plant parts — Effects of ultra-violet radiation upon 

 anatomical structure and flower formation — Ultra-violet radiation and the formation 

 of chlorophyll and anthocyanin — Concluding remarks. References. 



INTRODUCTION 



In trying to arrive at a definite understanding of the effect of ultra- 

 violet radiation upon plants one is immediately confronted by the fact 

 that few experiments have been conducted in which ultra-violet alone 

 was the causative variable. There is consequently little agreement 

 among the investigators. Furthermore, the beneficial effects of ultra- 

 violet on the animal organism have, in recent years, encouraged the 

 attempt to demonstrate similar effects on plants, with the result that 

 a great number of short experiments have been reported in which the 

 lack of adequate controls has rendered the conclusions of doubtful 

 value. In view of these facts the best that can be done in a review of this 

 kind is to point out the claims of the various investigators and to evaluate 

 them as far as possible on the basis of the merits and defects of their 

 methods. The discussion which follows is subdivided according to the 

 nature of the work reported. 



THE EFFECT OF ULTRA-VIOLET RADIATION UPON SEED GERMINATION 

 AND EARLY GROWTH OF SEEDLINGS 



EARLIER INVESTIGATIONS 



Before 1921 very few investigations had been carried out on the 

 effects of ultra-violet radiation upon seed germination and early growth 

 of seedlings. Carl (9) had stated that ultra-violet rays from a mercury- 

 vapor lamp were detrimental to seed germination and the early growth 



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