1909.] The ''Greening" of Potatoes. 179 



experiment, and when cooked had the sweet taste and close 

 texture characteristic of many potatoes in the spring ; whereas 

 the batch that had been thoroughly "greened " immediately 

 after lifting was quite " floury " and normal. 



Advantages of " Greening " — The time is now past when 

 small potatoes, good for nothing else, were considered good 

 enough for "seed." The general opinion held at the present 

 day is that it is essential to have a good, firm tuber that has 

 not been partly exhausted by loss of moisture and continued 

 formation of sprouts that are broken off when the tuber is 

 planted. As the above experiments indicate clearly, this 

 result is better attained with "greened" seed than with seed 

 not so treated. A potato not "greened" loses just over six 

 times as much in weight during the season as a potato of equal 

 weight that has been "greened." A potato that is "greened " 

 in the spring loses twice as much in weight as a potato 

 "greened" immediately after lifting in the autumn, other 

 things being equal. 



Effect of Action of Light on Growth. — Under similar condi- 

 tions of temperature, light much retards the growth or 

 sprouting of a potato, whereas growth is greatly favoured by 

 darkness. The explanation of this difference of behaviour 

 in light and darkness respectively is as follows : — Before a 

 potato can commence to sprout a certain amount of its starch 

 must be converted into soluble sugar by means of a ferment 

 or enzyme. Such enzyme can only be formed in a potato 

 when there is a free interchange between gases formed in 

 the interior of the potato and the atmospheric air. 



An experiment proved that when the surface of a potato is 

 coated with an impermeable varnish, except the "eyes," no 

 sprouting takes place, even under the most favourable con- 

 ditions for so doing. 



The act of "greening" causes the skin or periderm of the 

 tuber to become comparatively impervious to water and 

 gases, hence the relative cessation of growth and loss of 

 substance, whereas the periderm of a tuber kept constantly 

 in darkness is not so impervious. The difference in amount 

 of suberin present in the two cases is readily apparent on the 

 application of tests for the presence of this substance. 



The greatest amount of benefit derived from the "green- 



O 2 



