358 Miscellaneous. 



and from the adult female, L. ridihundus, in full summer plumage it 

 differed in the most trivial manner only. 



ON THE DISEASE OF POTATOES. BY PROF. KtJTZING. 



The diseases of potatoes have of late years attained so unusual an 

 extent of diffusion, that their investigation must become of universal 

 importance, especially when we recollect that this is the only means 

 of ascertaining the cause of the disease. 



During the presentyear a disease has appeared in the potatoes grow- 

 ing around Nordhausen with which the author of this communication 

 was not previously acquainted ; nor is it mentioned in the writings 

 which have in modem times treated of the diseases of potatoes. 



It is of a totally different nature from the so-called dry-rot (caries 

 of the tubers), in which the starch granules become so altered as to 

 exhibit minute brown fungi similar to those of corn- smut, and the 

 cellular tissue which surrounds these bodies becomes destroyed or 

 dissolved at a subsequent period only. In the disease of the present 

 year an alteration and solution of the cellular tissue alone is visible, 

 the starch granules remaining within it in a sound and unaltered 

 state. For this reason I have called it cell-rot. 



The cell-rot at first appears just beneath the cuticle of the tubers, 

 and always extends from thence towards the interior. It constantly 

 commences with a brownish discoloration of the substance, which 

 at first is still firm and solid, but gradually assumes a lighter and 

 darker colour until it is dissolved and forms a greasy, soft, dark brown 

 (sometimes verging to violet) mass, which possesses a foetid odour. 



On microscopic examination perfectly healthy starch granules 

 may be detected in all the stages of the disease, a proof that the 

 true nutritious ingredient is not destroyed by this change. But the 

 cells, which contain these starch granules, and which in the healthy 

 substance are clear, colourless and extraordinarily transparent, even 

 in the earliest stage of the disease appear of a yellowish colour, and 

 the membrane exhibits a finely granular structure which impairs their 

 transparency. As the disease progresses the colour and granular 

 structure of the surface of the cells increase, until at last they are 

 either partially or completely dissolved, the starch granules pass out 

 of them and become mixed with the decomposed mass. At this pe- 

 riod we find in the fluid decomposed cellular mass a fine filamentous 

 fungus, which frequently extends to the surface of the diseased cells, 

 and is diffused through the soft mass in a ramified form or united 

 into bundles. Its formation, as I have satisfactorily observed, is a 

 consequence of the decomposition of the cells, for it is not present 

 in the earliest stage of the disease. 



The cause of this disease appears to depend partly upon too great 

 an amount of moisture, partly on too copious a supply of manure to 

 the soil : both induce too rapid a growth of the tubers, which renders 

 the formation of a strong and durable cellular membrane impossible. 

 Moreover, all the potatoes which have experienced the cell-rot con- 

 tain a much lerger amount of aqueous constituents than the sound 

 ones. It may be expected that the disease of the tubers which are 

 laid up for winter store will extend itself und finally destroy them. 



