3^7 



of the seed and general depression in growth. The explanation of the phe- 

 nomenon should be sought in the physical domain. The ooze which is very 

 impervious to water and air, 

 because of its closely cemented 

 particles and its fatty content 

 arrests the spread of the roots 

 and greatly prevents the rise and 

 fall of the water. 



The Scurvy Disease. 



Among the many forms of 

 disease, of which the causes 

 are not satisfactorily explained, 

 scurvy should be included under 

 the diseases due to material ex- 

 cess. The reason for this is the 

 frequent observation that after 

 the addition of substances tend- 

 ing to increase the alkalinity of 

 a soil, scurvy usually appears in 

 increased amounts. 



Scurvy or "scab" consists 

 of flatly spread, cork colored 

 bark-like spots formed on the 

 fleshy under- 

 ground root, 

 or storage tu- 

 ber. As long 

 as such a bark- 

 like cleft re- 

 mains super- 

 ficial the dis- 

 ease is called 

 "surface scur- 

 vy." If, on the 

 other hand, the 

 injured places 

 deepen rapid- 

 ly becoming 

 grooves or 

 holes, the dis- 

 ease is called 

 "deep scurvy." 

 In certain 



cases warty outgrowths appear on the wounded surface, and this condition 

 has been distinguished as "knotted scurvy." 



Fig-. 52. 



Carrot diseased with deep scurvy, seen from the 

 most diseased side of the root. 



Fig. A. /, /' find t-. vascular bundle ring's arranged in terraces: g. holes in the 

 tissue with tinder-like eilt;es; k. tnl'erons parenchyma outgrowths on the carrot 

 head, which may be iiidiiMlnl as i)u- o\ irjrowtli ti-^'^iie of the scurvy wound: s, 

 initial stages of the s> m \ \ w liii li t \ti ii>l d^ .w iiwaid along the root groove (IV) : 

 r, outer edge of the scui\\ Imllcw: ., it-, ikii>cst pail; big. /?. Cross-section of 

 the carrot near the center of tlie deep scurvy U ) .■ Vascular bundle rings destroyed 

 by tlie scurvy i, i'- and t^ which extend outward like terraces from the deepest 

 part of the wound; / shows the poor formation of the outer vascular rings. 



