EFFECTS ON THE STRUCTURE OF THE TUBER. 



59 



paper be applied to the juice of a sound potato, it will give 

 a slight acid reaction; at the commencement of disease 

 this disappears, and the juice assumes a neutral character, 

 which speedily changes as 

 the disease progresses to an 

 alkaline, accompanied by 

 the well-known ammoniacal 

 odour of decaying tissues. 

 This change in the condition 

 of the tuber resembles that 

 described at p. 445, vol. i., in 

 reference to the peculiar form 

 of disease noticed in the man- 

 gold crop, and arises from the 

 nitrogenized portions first 

 undergoing decomposition, 

 ammonia being always one 

 of the first compounds formed. 

 Without attempting any 

 speculations as to the cause 

 of the potato disease, its effects are too marked and too ex- 

 tensively known to allow us to disregard it; and we 

 ought, all of us, to do our duty towards the community 

 at large by taking such precautionary measures in its 

 cultivation as common sense and past experience show 

 us to be likely to check its ravages. 1 There can be little 

 doubt that its existence is influenced greatly by the 

 physical conditions surrounding it, whether in its early 

 or its later development. We have been departing, for 



Transverse Section of Diseased Tuber 



largely magnified. 



1. Bark. 2. Cuticle. 3. Reservoir of 

 empty cells. 4. Diseased cells. 5. Channels 

 leading to "germs," or "eyes." 6. Cells 

 not diseased. 



1 In the Cyclo. of Agri., Mr. Berkeley discusses the various phases and pro- 

 bable cause of the disease; and in the pages of the Agri. Gaz. may be seen, not 

 only the results of the observations of many of our leading agriculturists at 

 home, but digests of the more important speculations or theories that have 

 emanated from the various scientific men as, Schacht, Spierschnieder, Boll- 

 man, Schleiden, Mitscherlich, Payen, Decaisne, and others Avho have investi- 

 gated its effects on the potato crops of the Continent. 



