64 RECAPITULATION. 



3. The ash of the potato is small, and in this respect again it resembles the cereals. 



Another peculiarity consists in the large percentage of potash, and almost total ab- 

 sence of lime and magnesia ; which shows a still further resemblance to the cereals. 

 In a few instances, soda has exceeded in amount the potash ; but as a general rule, 

 the proportion of potash amounts nearly to one half of the whole inorganic matter. 



4. I may once more refer the reader to the differences which exist between the parts of the 



potato, as exhibited in the analyses of the Mercer and Merino. The differences are 

 not confined to the water, but extend also to the alkalies and phosphates. These 

 differences meet perhaps with a partial explanation in the fact that the phosphates 

 and alkalies are not so much in combination with the solid parts (fibre), as in solution 

 in the juices. This appears from the fact that the fibre contains but a small propor- 

 tion of phosphates and alkalies. 



5. The fibre, however, must be regarded as a highly nutritive substance, and as well 



worthy of attention when the potato is used for starch. Indeed, animals which have 

 been fed upon it exclusively, have thriven and grown fat ; and hence as a matter of 

 economy, establishments for the manufacture of starch from the potato ought to un- 

 dertake the fatting of stock with the fibre, which is now too often regarded as an 

 entirely worthless article. 



6. I have made but partial examination of the condition of the diseased potato. It has 



been found, however, to contain more water, and less starch, than the sound tuber. 

 When placed in a posture favorable for the purpose, it dries rapidly. 



7. A comparison of the relative composition of the tops of potatoes is given in the analysis 



of the Early Shaw. In the tops, lime, magnesia and potash in the form of carbonates, 

 exist in their ash ; though as carbonates, they are merely the products of combustion, 

 being derived from organic acids, which, during ignition, are converted into carbo- 

 nates. The leaves and stem, when compared, present remarkable differences. The 

 leaves, for example, give a much larger per centum of ash. In the leaf I find a large 

 per centum of silex ; in the stem, much less. The leaf too is rich in phosphates, 

 particularly phosphates of iron and lime. In the stem, the phosphate of iron is but 

 little more than a sixth part. While a magnesian phosphate abounds in the tuber, 

 as in grains, it forms only a trifling element in the stem and leaves. 



There is an apparent anomaly in the proportion of water and ash in different parts 

 of the stem. Thus the percentage of ash seems to diminish from the root upwards, 

 while the water increases ; but in the leaves, the solid residue and ash is much greater 

 than in the bottom of the vine. In the stalks of ripe grain, the butt or base of the straw 

 contains less ash than the top. It will be seen that the alkalies prevail in the stem of 

 the potato, and the phosphates in the leaves. Soda, however, which is always pre- 

 sent in the tuber, is only found in traces in the stem and leaves. 



8. It can scarcely escape the observation of an attentive reader, that potato tops must form 



an excellent manure. They contain all the elements essential to the cereals ; and 

 hence it is that where the tops are left upon the soil to decay, the land does not im- 



