1 907.] 



Degeneration in Potatoes. 



387 



conveyed to the growing shoots through certain portions of 

 the fibro- vascular system, which appears to the naked eye 

 when a tuber is cut across, as a thin line forming a ring situated 

 some little distance from the surface of the tuber. Branches 

 from this ring pass outwards to the " eyes " or sunken points 

 from which the sprouts originate. Now the improvement in 

 the tubers, from the culinary standpoint, which has resulted 

 from these methods of selection and inter-breeding, has at the 

 same time been accompanied by a serious degeneration of the 

 nbro-vascular system ; in fact, in many examples that have 

 been examined microscopically this system is found to be so 

 much reduced, especially in the branches connecting the main 

 ring with the " eyes," as to be rendered incapable of conveying 

 the necessary amount of food from the tuber to the growing 

 shoots. Consequently the growing shoots are either not de- 

 veloped at all, or only developed as weakly branches devoid 

 of vigour and soon perishing. It is a well-known fact that a 

 quarter of a century ago, stored potatoes (even the varieties 

 most renowned for their " mealy" or " floury" qualities) were 

 apt to become sweet in flavour, watery, and unsuitable for table 

 purposes during the early spring months. Various methods 

 of treatment were devised for preventing deterioration from a 

 culinary standpoint, more especially in the case of potatoes 

 stored on board ship for use 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 composi- 

 tion until midsummer or even for a longer period of time. 



The primary obj ect of the mass of starch stored up in a tuber 

 is that of supplying formative material for the shoots during 

 their 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 



2 B 2 



