328 Journal of Agricultural Research voi.xx,No. 4 



The presence and activity of the blackleg organism results in a gradual 

 or rapid cutting off of the water supply from the roots and in a break in 

 the path of translocation for plastic materials in the lower stem region. 

 As a consequence of the decreased water supply, we have a decrease in 

 growth activities, especially a check in elongation. The newly formed 

 cells seem to mature more rapidly; in fact, mature and already strongly 

 lignified cells are found close to the growing apex. As long as the leaves 

 remain green and a minimum of water is insured synthesis of foods will 

 go on, though less extensively than in healthy plants. There is not, 

 however, an accumulation of starch as is commonly found in plants 

 suffering from leafroll, but there is a utilization of the food in the laying 

 down of extensive secondary thickenings in the cells of the xylem and 

 fibers and in a transformation of parenchyma cells into thick-walled 

 sclereids. Morse (6) reports that when the progress of the disease is 

 slow — 



numerous aerial tubers will be formed on the stalks at the surface of the ground or in 

 the axils of the leaves above. 



It would be of interest to know whether in such a case the same ana- 

 tomical changes occur which normally accompany blackleg. 



Just as the formation of sclereids is the most pronounced histological 

 symptom, the appearance of protein crystals in all organs of the plant, 

 the leaves in particular, is a cytological phenomenon always associated 

 with the disease. Protein crystals have been found in the tubers of 

 normal plants. Bailey (1) reports the occurrence of cubical crystals in 

 the tubers of Solarium tuberosum. A few years later Cohn (5) by the 

 use of protein reactions identified the crystals of Bailey as belonging 

 to the typical group. Heinricher (5) observed that in potato plants 

 where the root system had been destroyed by decay the basal portions 

 of the plant contained cubical protein crystals which were especially 

 abundant in the cells of the phloem but were altogether absent from 

 the cells of the epidermis and the collenchyma. Crystals have not been 

 found in the aerial parts of the normal plant, and in the researches of 

 the writer on the anatomy of the potato plant and the pathological 

 anatomy of the leafroll disease they have not been observed. However, 

 crystals have been noted by Stock (8) in aerial, axillary tubers, where 

 they show the same distribution in peripheral cells of the cortex as do 

 normally developed underground tubers. Protein crystals occur in great 

 abundance in all organs of "blackleg" plants, especially in the leaves 

 (PI. 57, B; fig. 1). The crystals are usually cubical and vary in size from 

 minute bodies to large structures with a diameter of two-thirds the size 

 of a palisade cell. They are normally found in the cell sap or in the 

 cytoplasm, very rarely inside the nucleus, although nuclear crystals, 

 according to the extensive researches of Zimmermann (9), are not at all 

 uncommon. 



