360 MANUAL OF OAl-XLE-FEEJDOTG- 



is in protein ; the more watery it is the less is its per- 

 centage of starcli, and the greater, as a rule, is the amount 

 of protein, and usually also of ash. 



When normally developed, the potato contains at lea^t 

 25 per cent, of drj matter, and the nutritive ratio is 1 : 10 

 -12. (jrown in a very rich soil or in a wet clay, the same 

 variety of potatoes contains far less starch, but is richer in 

 protein than when grown in a sandy soil or a sandy loam. 

 A soil rich in humus sometimes produces much larger 

 potatoes than a sandy soil, but their content of starch is 

 generally less than that of medium-sized tubers grown in 

 the same soil 



This variation in the percentage of starch according to 

 the size of the tubers, vanishes, the more closely the soil 

 approaches the sandy or loamy character, so that in po- 

 tatoes grown in such soils the content of starch often in- 

 creases with the size, especially if the smaller ones are not 

 fully ripe. 



It is also well known that the manuring exercises an 

 important influence on the quality and ehernieal compobi- 

 tioii of the potato. According to one observation, e, </., 

 the same variety of potatoes contained 2.27 per cent, of 

 protein when manured with potash and lime, and iA'i per 

 cent, when heavily manured with carbonate of ammonia. 



The same thing, however, is true of the potato as of 

 other crops, viz., that the influence of the manuring on the 

 quality of the crop varies according to the other influences 

 which act with it, such as soil, weather, ajid method of 

 culture. According to whether these aid or hinder the 

 action of a manure or chemical fertilizer on the compobi- 

 tion of the tubers, the effect produced will be more or less 

 striking. 



It may be added that the ash of Ihe potato is rich in 



