Nov. is, 1920 



Pathological Anatomy of Potato Blackleg 



329 



Nothing definite may be said in regard to the physiological importance 

 of these structures. Crystals have been observed in many plants, in 

 the fungi as well as the highly specialized angiosperms; but, while 

 certain groups of plants show them in great abundance, other plant 

 groups show just as conspicuous a 

 lack. Heinricher (5) believed that 

 the interception of the movement 

 of plastic material to the roots 

 causes a forcible deposition of the 

 protein in the basal parts of the 

 stem. This, however, could in 

 itself not account for their forma- 

 tion as has already been pointed 

 out by Stock (8), who observed 

 protein crystals in aerial tubers 

 but failed to find them in the stem, 

 although the cells in the latter are 

 completely filled with starch. The 

 crystals probably constitute transi- 

 tory food which may be used again 



in the metabolism of the plant FlG . , —Section of potato leaf, showing distribution 



and may accumulate when growth of protein crystals " 



is inhibited unless an excess of photosynthetic products (as starch in 



the case of leafroll plants) stops protein synthesis altogether. 



SUMMARY 



(1) Potato plants affected with blackleg show an increase in strongly 

 lignified vascular tissue and a transformation of part or most of the 

 parenchyma cells of cortex and pith into sclereids. 



(2) Associated with blackleg is the occurrence of protein crystals, 

 especially in the cells of the leaves. Under normal conditions protein 

 crystals have been observed only in the peripheral cell layers of the 

 cortex of the potato tubers. 



(3) Only diseased plants grown in the arid western parts of Colorado 

 have been studied. It is possible that plants grown in the eastern 

 United States and at a lower altitude do not exhibit the anatomical 

 changes reported in this paper. 



