14 AGRICULTURE OF MAINE). 



emphasize the importance of this viewpoint in approaching the 

 subject. It will not suffice merely to catalogue the diseases of 

 the potato and advise as to when to spray for each. Some more 

 fundamental notions are needed 'regarding the history and 

 development of the potato. 



The potato is the most commonly cultivated plant of our fields 

 and gardens. Yet it is the most variable in yield of our standard 

 crops and the most liable to diseases and failure from causes the 

 least understood. Why is this ? A partial explanation may be 

 found in the fact that it is a semi-tropical plant which has been 

 brought under cultivation in the northern climate by rapid and 

 intensive breeding. Our season of growth is shorter by one- 

 third, or even one-half than that of its natural habitat. There 

 it reproduces itself primarily by seeds, and secondarily by tubers. 

 Here, by breeding and selection, man has so changed the condi- 

 tions that seed production is almost unknown, while the size and 

 number of the tubers are enormously increased. 



For information upon these points I am largely indebted to 

 Mr. Cyrus G. Pringle, the veteran botanical explorer, who is 

 thoroughly acquainted with the potato, both wild and cultivated, 

 as it occurs in Mexico. In the gardens there it is planted in 

 March and harvested in December. The period of blossoming 

 and maturing of seed is in August and September, whereas the 

 tubers are formed one or two months later. 



Reproduction by seed is a sexual process, that by tubers is 

 vegetative. Both are exhaustive of vital forces. The two are, 

 therefore, in a physiological sense opposed, and cannot well be 

 carried on at the same time. Under the natural condition of 

 the wild plant the seed precedes. With our shorter season and . 

 intensive culture we have crowded the two processes together 

 until they tend to overlap. That is, we have forced the tuber pro- 

 duction back into the period which in the wild plant is given to 

 the production of flowers and seeds. As a result we have, just 

 after the potato plant comes into blossom, a strained and unnat- 

 ural condition : a state of physiological tension, of stress between 

 two opposing vital tendencies. According to the mode of its 

 ancestors the major part of the plant's energy would then be 

 tending upward toward flower and seed ; but tuber production in 

 the high-bred specialized plant begins immediately and the 

 acquired tendency is for this process to claim the major part of 

 the food. 



