4i6 



S. SAWA. 



For the experiment with algae, as Spirogyra, Mesocarpus 

 and diatoms, a 0.$% solution of potassium persulphate was 

 applied. 1 All these organisms died within one hour. Branches 

 of the rape plant about 17 cm. long with numerous buds showed 

 in the 0.$% solution of the same salt an injurious effect after 

 twenty-four hours : the leaves became curled, the tips of the 

 branches withered after three days and the lower part of the 

 branches bleached out. One day later the plants had entirely 

 died off. In the control cases with potassium sulphate and with 

 distilled water, the branches had remained healthy and many 

 of their buds had developed into flowers. The poisonous action 

 of the potassium persulphate on chlorophyl-bearing plants is 

 therefore plainly seen, but it is surprising to see that the poison- 

 ous action becomes very weak on a further dilution of the o-$% 

 solution to o.\%. In such a solution plum branches as well as 

 onion plants remained alive for a considerable time, although 

 some injurious action could be noticed. Thus only a few buds 

 of the plum branches developed within the next five days, 

 while in the control case with distilled water all the buds had 

 developed into flowers. After about ten days the branches 

 exposed to the persulphate seemed to be entirely killed. 



The onion plants remained alive considerably longer in the 

 OA% solution ; even after ten days only the tips of the leaves 

 showed signs of withering. Further growth seemed to stop ; 

 while in the control cases with potassium sulphate and with 

 distilled water alone it was not inconsiderable, as may be seen 

 from the following table. 



After the ten days of observation, all the necessary mineral 

 nutrients were added in the form of Knop's solution, and while 

 now the growth in the control cases was very marked, the 

 plants in the persulphate were very backward. One of these 

 plants showed a further drying up from the tip downward, while 

 with the other only a very insignificant increase was noticed 

 (see Table). 



1 In this case common well water was applied in preparing these solutions, to avoid 

 the poisonous action of the very minute trace of copper sometimes contained in distilled 

 water. 



