254 HIDEO KOJIÜEÜ. 



are parbicnlarly affected at the plumule and the mdicle. The metabolism of 

 these parts may be so gradually modified that at a certain stage the seedlings 

 cease to develop. 



II. Historical Survey of the EfiFect of Röntgen Rays 

 upon Higher Plants. 



RÖNTGEN discovered the X-rays in 1895 and two years after this discovery 

 LoPBlORE for the fii'st time studied their effect upon plants. Since then about 

 thirteen investigators have been engaged in the study of this problem. Now 

 the wiiter will shortly review these results in jjeriodical order. 



LomiOKE (1897) observed the fact that pollen-germination of Genista and 

 Darlimjtonia cwonUlcefoUa was suppressed by X-rays. 



Maldiney a- THOü\'ENrN (1898) espeiimented on the effect of Röntgen 

 rays upon Calystegia sepium and Oenanthe stoloni/era and found that germination 

 and growth were accelertited, but there was no effect on chlorophyll formation. 



Seckt (1902) stated that the acceleration of the protoplasmic movement 

 in the hah- cells of Tradescmifia and Cucurhila by iixadiation is similai" to the 

 effect of toxic suljstances and wound-stimulus on plant cells, and the eflect of 

 X-rays differs according to the distance between the tube focus aaid the material 

 to be irradiated and tlie time of exposme. 



KoERNiCKE (1904) exposed Vicia /aha, Vicia sativu and Brassica napus 

 to rays of 20 H-26 H — the material was yoimg plants and air-dried and steeped 

 seeds (3 days' steeping) — and oljscrved an impediment of growth except in 

 Brassica. There was no change at the time of irradiation, but the acceleration 

 as well as the impediment of growth appeared only after some time had 

 elapsed. These sj^jeciiil after-effects (Nachwh'kuug) are duo to the state of 

 the material and its phj'siological condition at the momenL of irradiation. 

 Brassica may have a resistance against the effect of X-rays ; there appearep 

 no conspicuous impediment of growth from a dose by which the growth of 

 Vicia faba was obsti'ucted severely. In the case of a not too sti'oug irradi- 

 ation, an impediment juay temporarily ap^jear, as the radicle, whose growth 

 was thei-eby stunted for a time, begins to develop again. Increase of germinating 

 power of air-ch'ied seeds was not obseiTed as in the case of stee]X!d seeds — 

 the exjDerimeut was re^xjated twice with tlie fonni-e dose of 20 H. 



