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during the prolonged voyages of that period. This defect is not 

 apparent at the present day, and many of the best kinds remain 

 unchanged in composition until midsummer or even for a longer 

 period of time. 



The primary object of the mass of starch stored up in a tuber is 

 that of supplying formative material for the shoots during theii 

 early period of growth until leaves are developed. Before the 

 starch can be utilised, however, it has to be converted into a 

 liquid condition, when it is conducted through the elements of 

 the fibro-vascular bundles to the growing-points. The solution of 

 the starch is effected by means of a soluble ferment called diastase, 

 which is produced in the tuber when the normal season for growth 

 or sprouting arrives. Now in many high grade potatoes at the 

 present day, diastase is produced in such small quantity that it is 

 incapable of converting more than a very small proportion of the 

 starch present into liquid sugar, hence the absence of sprouting is 

 due to a lack of the food material necessary for the work. For 

 the same reason many tubers remain almost unchanged as to starch 

 contents when the crop is lifted in the autumn. These are illus- 

 trations of somewhat extreme cases, but the fact that potatoes in 

 general remain ' floury ' for a longer period of time than formerly, 

 indicates a gradual and general loss of power on the part of 

 potatoes to produce the necessary quantity of diastase. 



Prunet's method (c) of determining the relative amount of 

 diastase present in potatoes is as follows. Absolute alcohol is 

 added to a definite amount of liquid pressed from crushed potatoes. 

 The precipitate thus formed is collected on a filter and dissolved 

 in a definite quantity of water. This solution, when added to a 

 known quantity of water containing starch paste in solution, 

 admits of the relative proportion of diastase present being deter- 

 mined by the rapidity with which the liquor ceases to be coloured 

 by a solution of iodine. 



By adopting the above method a total absence of diastase was 

 proved in the case of tubers that had failed to sprout. In other 

 examples the relative amount of diastase present was ascertained 

 to be in proportion to the number of sprouts formed. Diastase is 

 first formed, and in greatest abundance, at the apical or free end 

 of a tuber, and for this reason the earliest and most vigorous 

 sprouts are produced in this region in a normal tuber. When me 

 presence of diastase is on the wane it also lingers longest in tne 

 apical region ; hence, in a large percentage of deteriorating tubers, 

 sprouts from a single apical ' eye ' are alone produced, as in t lg. . 

 and in many instances, where the supply of food is very scanty 

 owing to the absence of diastase, these sprouts perish at a ^e ry 

 early age, as shown in Fig. 2. In Fig. 3, which i lus rate the 

 grower's ideal even surface -a factor of undoubted value *h en 

 the loss resulting from paring is the object in view-the powe ict 

 growing or sprouting has been completely lost, owing to deteriora- 

 tion of the fibro-vascular system and the comparative absence of 

 diastase. 



During the past three years a series of experiments *»™ **«* 

 conducted with the object of imparting new vigour to potato** 



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