370 



connection of the scurxy disease with parasitic organisms, which, ne\er- 

 theless, are not specific scurvy organisms. It is much more probahle that, 

 in beet soils, saprophytic species, which are generally present, are able, be- 

 cause of definite changes in the composition of the soil, to attack weakened, 

 old beets, or tender young ones. The fact that the healthy vascular bundle 

 rings are more slender where scurvy began, i. e., their growth in breadth has 

 been retarded, proves that the beet has undergone arrestment during the 

 time of the scurvy disease. 



Supported by Bolley's inoculation experiments' which ])rove that beet 

 scurxy and potato scab are due to similar causes, we will t;)ke up the main 

 question, viz.. what conditions have been determined practically as favoring 

 or causing scurvy. It is well known among agriculturalists that marling the 

 field results most frec|uently in an attack of potato scab. The yellow marl, 

 which contains magnetic oxid (Fe., O^) is said to be the most dangerous. 

 Frank has conducted cultural experiments'- to determine the problem. 

 .Scurvy is produced on unsterilized soil, but not on sterilized, even 

 when loamy marl is added tf) it. As sliown by ','xperiencc. meadow 

 ore. street sweepings, sewer muck, fresh animal manure, liciuid manure and 

 Chilean saltpetre all favor scurvv. which fact enforces the decision, that (//' 

 alkaline reaction affords the most favorable conditions for the development 

 of scurvy f)rganisms. Bolley' also arrives at this conclusion. His experi- 

 ments show that the scurvy bacteria which he used develop most rapidly on 

 neutral or basic nutrient soils. T-Vank's comparative experiments ])ro\c 

 that moisture acts favorably, and Bolley emphasizes the observation tint 

 light, sandy soils, as a rule, yield smooth tubers. Frank's results seem to 

 contradict the observation that a good deal of scurvy can lie found in some 

 places in hot, dry years. 



These apparent contradictions are explained by Thaxter's investi- 

 gations*. He distinguishes between organisms causing the deep scurvy and 

 those causing superficial forms and empliasizcs his conclusion that a i-'c-utral 

 reaction seemed most favorable for the organisin which lie cultivatei. 

 Slight alkalinity, however, like slight acidity, seemed to have a retarding 

 effect. In his experiments young tubers were attacked at any place, older 

 ones on wounded surfaces and especiallv on lenticels, while nearly ripe 

 tubers were entirely free. 



All scurvy organisms, therefore, do not seem to require the same C(M1- 

 ditions. In common, how'ever, they prefer lenticels and young organs with 

 a delicate cork covering. In beets, the places where the rootlets arise are 

 especially suitable as points of attack for the micro-organisms. These 

 places become very much broken in wet soils, and this fact explains the 

 assertion that moisture favors the development of scurvy diseases. Wet, 



1 Bolley, H. I^., A. disease of beet.s. identical with deep seal) of potalfies. Gov. 

 Agric. Exp. Stat. f. North Dakota. Bull. 4, 1891. 



- KamiJfbuch segen die Sohadlinge unserer Feldfriichte. 1897, p. 177. 



3 Zeitschr. f. Pflanzenkiankh. 1901. p. 43. 



•t Thaxter, Roland, The Potato Scab. Fourteenth Annual Report of the Con- 

 necticut Agric. Exp. Stat. 1890. 



