492 SiLBERBERG : STIMULATION OF STORAGE TISSUES 



clean filter paper, and placed in the glass dishes previously pre- 

 pared. 



Examination to determine results was made by cutting sections 

 of the cylindrical specimens, always about 5 mm. from^ the end. 

 The sections were mounted in water and examined immediately 

 after mounting. 



Part I 



Before making any experiments with zinc sulphate, several 

 kinds of tissue were tested for their power to* produce callus and 

 meristem under the conditions to be used for the control. It was 

 found that AIUudi Cepa (onion) could not be used because it 

 decayed in the moist atmosphere. Radicnla Armoracia (horse- 

 radish) formed a suberized layer with meristematic tissue inside it, 

 but was so susceptible to moulds that its use was abandoned. 

 During the course of the experiments, Brassica Rapa (turnip) 

 was tried, but it, too, proved unsatisfactory, because it was too 

 easily affected by moulds and rot. Heliayithis tuberosns (Jerusa- 

 lem artichoke) was experimented with at the same time, but did 

 not give the desired response, Datictis Carota (carrot) formed 

 callus but so very slowly that it was considered unfavorable for 

 experimentation. After this process, of elimination, those which 

 at first appeared to lend themselves favorably to the work in hand 

 were Beta vulgaris (beet), Ipom^a Batatas (sweet potato), Brassica 

 oieraceaQ^ohl-vdH), Sol a ninn tuberosum {^otz-to), and, later, Trago- 

 pogon porrif alius (salsify). Of these the potato was quite the most 

 satisfactory. 



The sweet potato, which formed callus very readily at first, 

 proved to be very suspectible to rot. It was probably due par- 

 tially to this that the results obtained were so variable that they 

 could not be used as a basis for any conclusions. 



The beet, also, which seemed very desirable in the preliminary 

 tests, did not form callus so readily after the experiments had been 

 in progress for a few weeks, but dried out so much as to be use- 

 less for examination. When this trouble was encountered, freshly 

 grown Bermuda beets were secured, but they gave no better satis- 

 faction than the old ones. The results that were obtained, as in 

 the case of the sweet potato, were so variable that no conclusions 



