No. 4.] 



PLANT DISEASES. 



29 



such parallelism, but instead a marked contrast between the 

 two plants in almost every particular. 



Siommary contrasting the History and Development of the Potato with 

 that of the Ajyjflc. 



Apple. 



1. Culture antedates recorded history. 



2. Original home i:i north temj)erate 



regions of Asia and Europe. 



3. Season like our own ; climate dryer. 



4. It is fully acclimatized and domesti- 



cated as cultivated here. 



5. It has not been modified in its essen- 



tial life processes or structures. 



6. Its normal sexual reproductive proc- 



esses leaduig to seed formation re- 

 main unimpaired. 



7. It is a long-lived tree. 



8. Therefore, but slightly and slowly 



affected by unfavorable environ- 

 ment (soil and atmosphere) . 



9. 



Varieties have great stability, dete- 

 riorating but slowly, if at all. 



Potato. 



1. Culture relatively modem. 



2. Original home on the plateaus of 



tropical or sub-tropical America. 



3. Season much longer than our own ; 



climate moister. 

 i. It remains a half-wild foreigner 

 still. 



5. It has been fundamentally modified 



in its essential life iirocesses and 

 structures. 



6. Sexual (seed) reproduction is almost 



lost, and the vegetative i^rocess 

 (tuber formation) substituted. 



7. A short-lived herb, perennial by 



tubers. 



8. Liable to quick-acting and even fatal 



diseases associated with unfavora- 

 ble environment (soil and atmos- 

 phere) . 



9. Varieties unstable, and deteriorate 



or " rim out " in a few years. 



The conclusions from the above comparison may be summed 

 up by saying that, whereas the apple as we have it in culture 

 is in stable equilibrium structurally and physiologically, the 

 potato is in most unstable equilibrium. As a practical result, 

 the potiito is of all our sta})le farm and garden cro})s the most 

 liable to destructive diseases, of which the causes are most 

 complicated and the fundamental remedies the least under- 

 stood. 



The full justification of this conclusion requires a some- 

 what more detailed consideration of the facts we have sum- 

 marized above. 



The potato is a semi-tropical plant, which has been brought 

 under cultivation in our northern climate by rapid and inten- 

 sive breeding. Its ancestors occur as natives in the Andean 

 plateaus of South America, and as far north as Mexico. For 

 advice on the latter point I am indebted to my associate, 

 Cyrus G. Pringle, the veteran botanical explorer of Mexico, 

 who finds the potato there both wild and half domesticated, 



