THE POTATO IN BRITISH COLUMBIA. 



15 



QUALITY IN POTATOES. 



Varieties of potatoes differ greatly in their cooking qualities. In Canada a 

 mealy potato, white and floury in colour, is more desirable than one coloured or 

 soggy after boiling. 



Mealiness is directly associated with a high starch content. The grains of 

 potato-starch expand and coalesce when boiled in water, and if the cells are 

 sufficiently full of these bodies the boiling will cause the cellular structure to be 

 broken down, which results in mealiness. 



In a potato of poor quality sufficient starch is not present in the cell, Jind 

 therefore its walls are not broken down in cooking; hence we have a soggy potato. 

 The following factors are considered to influence the quality of potatoes: 

 (1.) Type of Soil. Potatoes grown on a peaty soil do not possess the cooking 

 quality of those grown on a sandy loam, because the rapid growth which the tubers 

 make in peaty soils is likely to bring about watery tubers. 



(2.) Degree of Maturity. Potatoes are of the best quality when they have 

 been fully matured, because the starch has been more fully developed. From this 

 the need for a long growing season will be appreciated. 



(3.) Storage. Potatoes lower their 

 starch content in storage because 

 enzymes work on the starch. 



(4.) Soil-moisture. Since moisture 

 is a factor which influences the quality, 

 the necessity for planting deep in dry 

 soils, also constant use of the cultivator, 

 is evident. 



(5.) Disease. Growth is often 

 checked by disease such as "blight"; 

 this can be overcome by proper spray- 

 ing. 



(6.) Secondary Tubers (Fig. 7.) 

 This is a common occurrence in irri- 

 gated districts, because irrigation-water 

 is applied at the wrong time. Irriga- 

 tion-water should never be applied after 

 bloom-time. The secondary tubers are 

 due to the fact that at some period 

 during their growth they were dried 

 out, becoming partially ripened. Irri- 

 gation-water is added and growth again 



commences. The new growth takes the form of lumps. These potatoes are undesir- 

 able, as there is great waste in peeling and the cooking quality is' lowered. 



Certain external and internal features of the potato are associated with quality. 

 The following are the chief features: 



(1.) The Skin. An uneven surface with deep eyes is undesirable. A netted 

 skin indicates maturity ; therefore good quality. A smooth skin indicates a degree 

 of immaturity ; hence poorer quality. 



(2.) Tubers are of poor quality where cortical layer is thick and dense. 

 (3.) Uniformity of external medullary area indicates an even distribution of 

 starch in the cells. Non-uniformity indicates watery areas, and therefore poorer 

 quality. 



(4.) A large and branching medullary layer is an indication of more water 

 than starch. When it is small less water and more uniformity in the starch is 

 indicated, and therefore better quality. 



4 



Fig. 7. An extreme case of second growth 

 (original). The use of such potatoes for seed 

 should not be tolerated. 



