104 POTATO DISEASE. 



We must not suffer ourselves to be misled by apparent or shal- 

 low analogies. The bane of vegetable physiology has been, and to 

 a great degree still is, the assumption that plants are in this or that 

 respect like animals. The "circulation of the sap," its " elabora- 

 tion in the leaves," the "stagnation of juices," are specimens of 

 ancient speculation that infest our text-books in the school, and 

 our hand books iu the orchard or vinery. 



They are the scape-goats of learned ignorance, the last resort of 

 wisdom that is never at a loss to render a reason. They serve 

 the psuedo scientific cultivator the same office which Semmes' 

 Hole performs to the stay-at-home Arctic Explorer — are an inac- 

 cessible and bottomless pit, large enough to engulph all difficulties. 



The other objections raised by J. G. W. to the fungus theory, 

 remain to notice. The first difficulty he suggests is, that two kinds 

 of potatoes are unequally affected We explain this as has been 

 intimated, by the fact that the cuticle and cell tissue of the hardy 

 kinds are thicker and denser than in the delicate varieties, as 

 Schacht has observed in the case of Klotzsch's Bastard. 



The second difficulty suggested by J. Gr. W. is, "that potatoes 

 grow and are dug and are rotten in seasons so dry that the earth 

 is never wet down so far as the potatoes in the hill. Especially 

 does this absence of wet often exist during the interval between the 

 appearance of the disease upon the leaf and upon the tuber." De 

 Bary distinctly states that the spores penetrate a moderately wet 

 soil. A slight rain or heavy dew, succeeded for some time by 

 cloudy close weather, which hinders the drying of the surface, 

 probably provides the conditions necessary for the fungus to reach 

 the tubers. If the fungus is in the tubers, it can't well be doubted 

 that it in some way reached them, although the precise mode or 

 conditions of access be but imperfectly understood. The fact 

 which I have observed, that deep-lying tubers may be perfectly 

 sound, while shallow ones of the same kind are entirely rotten, 

 accords with the supposition that the spores penetrate easily to 

 some depth, but do not pass beyond a certain limit. 



As to the rotting iu the collar, of potatoes which at the time of 

 digging were apparentlxj sound in tops and tubers, — this would 

 happen if the plants were moderately infected at harvest, and then 

 were carried into a damp cellar, especially if the tubers were 

 thrown into large heaps or placed in deep bins. The fungus spores 

 did undoubtedly remain concealed and inactive in the tubers, until 



