254 GROWTH OF PLANTS 



Thiourea prevents the browning of cut surfaces of fruits and other plant 

 organs by inactivating the peroxide of the tissue. One dip of the cut organs 

 in a 0.05 to 0.1 per cent solution is sufficient to prevent the browning of 

 fruits for drying and freezing, and for salads and sliced desserts. In high 

 dosages thiourea has goitrogenic action and reduces hyperthyroidism, 

 but the dosages that can be consumed in treated fruit are very far below 

 these therapeutic doses. The lethal dose of thiourea for mammals is even 

 higher than that of table salt. 



Methyl ester of a-naphthaleneacetic acid proved very effective in inhibit- 

 ing the gro\vth of potato buds. Tubers treated with 25 mg of this ester 

 appUed in talc powder to a kilogram of tubers inhibited the growth of the 

 buds so the tubers could be stored at 10° C (50° F) or even higher for more 

 than a year without sprouting or shrivelling. In the fully inhibiting dosage 

 the tubers absorb about five-millionths of their weight of the chemical and 

 four-fifths of the chemical absorbed is held by the skin. The chemical has 

 a low order of toxicity for mammals. This discovery should prove of great 

 value in farm and commercial storage of potatoes. 



After two to three weeks of cold storage, dormant gladiolus corms can 

 be forced by ethylene chlorhydrin vapor treatment. The cormels are more 

 dormant, but many varieties are fully after-ripened by storage at 5° C (41°F) 

 during the winter. The cormels of other varieties are more dormant and, 

 in addition to low-temperature storage during the wdnter, require ethylene 

 chlorhydrin treatment for a high percentage of germination. The produc- 

 tion of corms of desirable dormant new varieties can be greatly accelerated 

 by ethylene chlorhydrin forcing of cormels. 



Corms of gladiolus can be held dormant and in good condition for eight- 

 een months or more if immediately after harvest they are placed and kept 

 in moist soil at room temperature or preferably 27° C (80° F). Such corms 

 are thrown into active gro^vth by a few hours' exposure to 5° C (41° F). 



Buds of dormant deciduous trees and shrubs can be thrown into vigorous 

 growth in the fall by treatment with vapors of ethylene chlorhydrin, alkyl 

 halides, and other volatile chemicals. If only one bud is exposed to the 

 effective chemical it alone grows, showing that the dormancy dwells in the 

 individual buds. 



Even more effective bud forcers are being sought by using other chemicals 

 in combination with ethylene chlorhydrin in the hope of synergistic action 

 of the chemicals. 



Ethylene chlorhydrin disappeared from potato tubers faster than could 

 be accounted for by evaporation alone. It is tied with glucose in the potato 

 tuber and gladiolus corm, forming a less toxic glucoside. Several different 

 foreign more or less toxic chemicals, when supplied to plants, are tied up 

 with various sugars forming less toxic glycosides. This seems to be a means 

 that plants have of rendering innocuous poisonous products of their own 

 metabolism and certain foreign poisonous chemicals when absorbed. When 

 tobacco plants were furnished chloral hydrate in the nutrient solution they 



