232 



GROWTH OF PLANTS 



found two chemicals, ethylene chlorhydrin (CICH2CH2OH) and thio- 

 cyanates (K, Na, or NH4) that are very effective in throwing potato buds 

 into prompt growth. The first proved especially desirable because there is 

 a wide margin between forcing dosage and toxic dosage; moreover, as it 



r 



Figure 84. Effect of dip treatment of potatoes with 40 per cent ethylene chlorhydrin 

 after dipping tubers left in a closed container 22 hrs. Left to right: check, dipped in H2O; 

 dipping solution, 15 cc per liter; dipping solution 30 cc per liter. 



is soluble in water and has a high vapor pressure, it can be used either for 

 dip or vapor treatment. The thiocyanates have a narrow margin of dosage 

 and must be used by a soak treatment. Fig. 84 shows the effect of ethylene 

 chlorhydrin and Fig. 85 the effect of sodium thiocyanate upon the growth 

 of dormant potato tubers. These treatments completely eliminate the need 

 of the rest period, that is, the dormant tubers treated with the chemicals 

 grow with as high vigor and apparently give as high crop yields as time- 

 after-ripened tubers; unlike the hormone-like chemicals discussed in pre- 

 vious chapters, they do not produce any formative modifications in the 

 resulting plants, such as partial or complete anesthesia, extra root forma- 

 tion, modification of leaves and stems, and parthenocarpy. They merely 

 activate the normal growth of dormant buds. 



Figure 85. Effect of sodium thiocyanate solution upon the germination of freshly 

 harvested potato tubers. Cut tubers soaked one hour. Left to right: check (H2O); 34 per 

 cent; 1 per cent. 



By treatment of dormant tubers just after harvest, new sizable tubers can 

 be produced before dormant untreated tubers have germinated (Fig. 86), 

 so that several crops of potatoes can be produced in a year. This has been 

 very useful to potato breeders, who can hurry tuber multiplication by elimi- 

 nating the rest period and to plant pathologists who are studying potato 



