SOME CONDITIONS INFI^UENCING GROWTH 9 



related with the mode of development. If the soil is 

 very dry, and particularly if the tuber is cut, the seed 

 tuber may be so weakened by loss of moisture that it 

 cannot grow. If a tuber has access to but a small 

 amount of water, there will be little or no root devel- 

 opment, with little formation of leaf shoots, but tubers 

 will be formed. Advantage is taken of this fadt when 

 small earl}' potatoes are required, the tubers being 

 placed in sand, in a cellar, when small tubers will form, 

 but none or few leaves. Under certain conditions, with 

 an abundance or excess of moisture, numerous leaf 

 shoots and roots appear, but no tubers. An increase 

 in the supply of moisture in the air has been found to 

 favor the development of leaves on the shoots, where 

 only scales were formed in an insufficient supply of 

 moisture. 



Respiration. — We may say that all plants breathe 

 or take in oxygen and give off carbon dioxid. With 

 potatoes this is a necessary fun(5tion, and if checked, 

 growth is injured. It is probable that light induces 

 some conditions more favorable to increased respira- 

 tion than darkness; hence, if the object is to store pota- 

 toes, it will be better to hold respiration at its lowest 

 point and keep them in the dark. Respiration cannot 

 go on without force or energy, and as this must be 

 supplied, at least partly, from the tuber, it follows that 

 active respiration will be attended by loss of weight, 

 and this goes on very rapidly when the tuber sprouts. 



If we wish to ' ' sprout ' ' tubers, the best conditions 

 for doing so are still undetermined. 



Influence of Temperature on Respiration. — 

 All plants have a range of temperature at which respi- 



