EFFECTS ON HISTOLOGY 837 



leaves. The contents of palisade cells were drawn away from the upper 

 ends of the cells and the injury to the newly formed leaves was evident 

 throughout the entire leaf. Not only were the air spaces fewer but there 

 was much less differentiation between different kinds of cells, suggesting 

 that ultra-violet treatment may retard growth in individual cells, even 

 though they escape destruction. This work suggests that the penetra- 

 tion of some of the unscreened ultra-violet radiations may extend through 

 the entire leaf. 



The histological details of sections of leaves of Lactuca saliva, Nicoti- 

 ana Tabacum, Phaseolus vulgaris, Cucumis sativus, Ipomoea Batatas, Zea 

 Mays, Coleus Blurnei, and one of its varieties are included in the illustra- 

 tions of the plates. These are all consistent in showing a distinct correla- 

 tion of the degree of injury with the severity of the treatment under the 

 different conditions of the experiment, but it is hardly possible to con- 

 clude that all observed effects may be attributed exclusively and with 

 certainty to the action of the ultra-violet radiation. 



Where "vita" glass was used, screening out rays of less than 2900 A 

 wave-length, the general results were reported to be beneficial to the 

 plants. There were no lesions, though the newly formed leaves of several 

 species {Lactuca, Raphanus, and Coleus) were thinner than the controls. 

 Some plants had leaves thicker than the controls but in these cases the 

 treated plants themselves were larger. Under "vita" and "quartz-lite" 

 glass Coleus plants showed not only an increase in growth, with a corre- 

 sponding increase in leaf thickness, but also a complete retention of the 

 red pigment. The effect of filtered ultra-violet on stems resulted in 

 greater diameter and better developed vascular bundles. 



Nadson and Rochlin (23, 24), using a Bach model ultra-violet lamp, 

 in treating Pterygophyllum and two species of Elodea, exposed at 30 cm. 

 for 10 to 30 min., obtained crystals of calcium oxalate, formed within the 

 cells. These crystals which were observed in some cases as beginning 

 around the chloroplasts, increased in size and dissolved simultaneously 

 with the death of the cell after 2 to 4 days. Treatment of the plants with 

 narcotics before raying resulted in no crystal formation. Likewise, 

 Beauverie and Cornet (2) studied the effect of various lengths of treat- 

 ment of Elodea with the radiation from a quartz-merciiry-vapor lamp on 

 the cell contents. A treatment of 10 to 30 min. at 4 meters distance gave 

 no morphological changes after 45 min. or more of treatment. Granula- 

 tions were produced in the chloroplasts of individual cells, while in the 

 cells of others they remained hyaline. Treatment for 4% hr. gave a 

 change in the cytoplasm, a swelling of the granular mitochondria and 

 chondrioconts, though some of the chloroplasts were still intact. 



Martin and Westbrook (21) continued the work on periodic treatments 

 begun by Delf , Ritson, and Westbrook (8) by introducing further refine- 

 ment in the technique. They standardized their dosages in terms of 



