EFFECTS ON HISTOLOGY 835 



stated that this injury was locaUzed in the epidermis, since microscopic 

 examinations revealed that the surface layer had collapsed. The col- 

 lapse of these cells was explained as due to a loss of water from the epi- 

 dermal cells to the more active chlorenchyma cells beneath. 



Maquenne and Demoussy (20) repeated Deherain's experiments with 

 a quartz-mercury-vapor lamp. By means of plasmolytic tests they 

 showed that the epidermal cells were killed, but that the palisade cells 

 of the interior of the leaf remained uninjured. 



Hertel (11), one of the earliest investigators to experiment on the 

 effects of ultra-violet radiation on bacteria and other microorganisms, 

 also made some microscopic examinations on the effect of the magnesium 



o 



line (2800 A) on the cells of living Elodea canadensis. He reported the 

 cessation of protoplasmic streaming and death of the treated cells. 

 The killing effect on the epidermis of seedlings by ultra-violet radiation 

 was further confirmed by Stoklasa (36) who pointed out that the greening 

 of etiolated seedlings was hastened by exposure to the ultra-violet radia- 

 tion employed. 



In a series of investigations on the effect of ultra-violet radiation 

 on higher plants (Aucuha japonica, Echeveria sp., and Sempervivum sp.) 

 Kluyver (15) used a quartz-mercury-vapor lamp (range 90 to 220 ^olts, 

 usually operated at 100 volts and 3.5 amp.). He subjected his plants to 

 a single exposure of the radiation and discovered the latent effect, that 

 the reaction of his plants to the ultra-violet treatment would begin to 

 show some time after the exposure. He found also that short treatments 

 would kill only individual cells of the epidermis and that the lower epi- 

 dermis is more vulnerable to ultra-violet than the upper. The guard 

 cells of the stomata require longer treatment than ordinary epidermal 

 cells, and the subsidiary cells which adjoin the stomata, though otherwise 

 unrecognizable from their form, become recognizable from ordinary 

 epidermal cells as chemically differentiated structures by their less sus- 

 ceptibility to ultra-violet. 



Kluyver also investigated the effect of ultra-violet radiation on antho- 

 cyanin. After ascertaining that the extracted anthocyanin remains 

 stable after exposure to ultra-violet radiation, he found that living cells 

 of a Begonia leaf, except those at the veins of a leaf, which are covered by 

 an additional layer of coUenchyma cells, lose their anthocyanin with the 

 death of the epidermal cells. Other experiments on anthocyanin in 

 leaves as affected by ultra-violet rays are given by Schanz (30). 



After prolonged treatment of stems such as those of Phaseolus multi- 

 fiorus, Kluyver found that all of the cortical tissues on the exposed side 

 of the stem collapsed. The xylem cells on the same side gave less lignin 

 staining reaction (phloroglucin and hydrochloric acid) than did those 

 on the unexposed side, and the bast fibers of stems with bast were 

 similarly affected. 



