836 BIOLOGICAL EFFECTS OF RADIATION 



While Kluyver and previous investigators subjected plants to a single 

 exposure of ultra-violet and studied the subsequent effect on the plants, 

 we find other records of the exposure of plants to continuous irradiation. 

 Raybaud (29) grew cress seedlings (Lepidium sativum) with continuous 

 exposure under a quartz-mercury-vapor lamp at 1.5 meters and obtained 

 the epidermal killing effect reported by others as well as changes in the 

 deeper tissues. The dead epidermal layer served as a protection to the 

 deeper layers from the harmful action of the rays, but as subsequent 

 growth ruptured the epidermal cells, the exposed cortical cells were killed 

 in turn. The cortical cells of the hypocotyl were so affected that they 

 divided periclinally and elongated on the side exposed directly to the 

 light, with a consequent curvature of the hypocotyl toward the opposite 

 side. Deeper and deeper layers of cells were destroyed as the surface 

 became reticulated and opened into longitudinal furrows or grooves. 



Delf, Ritson, and Westbrook (8) exposed plants {TrifoUum, Voandzeia, 

 Pelargonium, etc.) periodically (several minutes daily) to the radiations 

 from a quartz-mercury- vapor lamp and obtained effects similar to the 

 previous investigations — collapsed epidermal cells followed by rolling and 

 distortion of the leaves during subsequent growth. They obtained these 

 effects on Voandzeia suhterranea after only three daily exposures of 2 min. 

 at a distance of 3 ft. 



Dane (5), who treated soy beans with ultra-violet, reported the stems 

 1.5 times as great in diameter as control plants. The rayed stems were 

 hollow and showed a reduction in the width of the medullary rays. Most 

 of the ordinary parenchymatous tissue of the medullary rays developed 

 into vascular tissues — xylem and phloem. The plants which were 

 exposed were more stunted and their tissues stiff and brittle. 



Eltinge (9) investigated the effects of periodic treatments on a great 

 variety of seed plants by dosages which began with 30 seconds exposure 

 the first day and were increased by this amount daily. The ultra-violet 

 radiation source was a uviarc quartz-mercury lamp emitting rays from 

 5780 A down to 2000 A. This lamp was used in a series of experiments 

 at 50 and 100 in. both with and without glass filters. The filters used 

 were "vita" glass (transmitting 5780 to 2890 A) and "quartz-lite" glass 

 (transmitting 5780 to 3136 A). Leaves were taken for anatomical study 

 from the unscreened series at the end of 4 weeks; at the end of 8 weeks 

 samples of leaves and stems were taken from all plants, which were killed 

 with medium chromic acetic killing fluid and sectioned in paraffin. Some 

 were stained in Haidenhein's iron alum haematoxylin and others with 

 safranin — Delafield's haematoxylin for microscopic study. 



Many anatomical details are described in this paper. Injury was 

 greatest in the unscreened series with an early deadening of the epidermis ; 

 where occasional epidermal cells escaped the killing they were distinctly 

 smaller. The anthocyanin pigment disappeared in all parts of stems and 



