286 PATHOLOGY [Box. Absts., Vol. X, 



1874. Weimer, J. L., and L. L. Harter. Wound-cork formation in the sweet potato. 

 Jour. Agric. Res. 21: 637-647. 1921. — Under favorable conditions a cork-laj^er forms over 

 wounds of the sweet potato {Ipomoea batatis). The production of this layer is preceded by 

 the formation of a layer of starch-free cells, usually 3-10 cells deep, beneath the injured sur- 

 face. Septa begin to appear from the 2nd to the 3rd day, and after 4-6 days a distinct layer 

 of cork cells covers the wound. The process takes place between 19.5 and 33°C., the optimum 

 being 33°. High humidity, 95-100 per cent, is favorable for cork formation; lower limits are 

 not reported. The conditions existing in the storage house did not permit of the formation 

 of a well developed cork-layer, but a hard, dry surface covering did develop through which 

 infection by artificial means could not be secured. The healed surface of a wounded sweet 

 potato also forms a fairly efl&cient barrier against infection by microorganisms. — D. Reddick. 



DESCRIPTIVE PLANT PATHOLOGY 



1875, Aoi, K. Reddish coloration of polished rice caused by Oospora sp. [In Japanese.] 

 Bull. Imp. Cent. Agric. Exp. Sta. [Nishigahara, Tokyo, Japan] 45^: 29-69. PL 1-3. 1921.— 

 In north Japan, polished rice, imperfectly dried, frequently becomes purplish red in storage. 

 Various molds and bacteria were isolated from such rice discolored during the summer of 

 1917 at Sakata, Yamagata, Japan, a large rice distributing town in the north. Infection 

 experiments with pure cultures of the isolated organisms on sterilized polished rice demon- 

 strated that Oospora sp. is responsible for the discoloration. When sterilized polished rice con- 

 taining 18 per cent water is inoculated with this species and left 4-7 days at 25°C., the dis- 

 coloration appears. Morphologically the fungus is comparatively simple, the differentiation 

 of fertile, nutritive, and vegetative hyphae being rather obscure. The nutritive (long) 

 hyphae, found chiefly in the medium, are divided by septa into numerous segments. The 

 vegetative hyphae grow almost exclusively on the surface of the medium and multiply by 

 budding to form yeast-like colonies on the surface of the culture medium. Fertile hyphae 

 arise from various segments and form conidia. Conidia are also produced by budding on the 

 free ends and sides of nutritive hyphae. The mature conidia are short, elliptical, 3-om in 

 diameter, and contain usually 1-10 refringent oil globules; germination is by budding. When 

 the fungus is grown on polished rice containing less than 19,6 per cent water, it assumes a 

 purplish red color; but on rice containing more water it becomes dark or even black in color. 

 No pigment can be extracted by water, alcohol, ether, benzene, benzine, or other ordinary 

 solvents. The purplish coloration is changed to reddish purple by alkaline solutions, and 

 restored by acids. By reduction with nascent hydrogen the color soon disappears. On 

 cooked rice (Japanese "Meshi") and on culture media, the colonies assume first a yellow 

 color, but gradually turn dark or black. Temperature limits of growth are 11 and35°C., the 

 optimum being about 25°. The minimum water content of rice which permits fungus growth 

 is about 15.5 per cent. On sound, unpolished rice the fungus does not grow, and on polished 

 rice having a water content less than 20 per cent growth is slight. Conidia of the fungus were 

 killed by several hours' exposure to direct sunlight in summer, and by 48 hours exposure to 

 air saturated with carbon bisulphide. But in lower concentrations, viz., 4 pounds carbon 

 bisulphide per 1000 cubic feet, growth was only partially retarded. — S. Hori. 



1876. Beach, W. S, The lettuce drop due to Sclerotinia minor. Pennsylvania Agric, 

 Exp, Sta, Bull. 165. 27 p., 3 pi., 3 fig. 1921. — Part I contains a historical review of this dis- 

 ease, which is similar to that caused by S. libertiana though differing from the latter in that 

 the sclerotia are much smaller and form crusts on the under surfaces of the lower leaves. 

 Meteorological and environmental relationships show that the disease occurs under a wider 

 range of environments than S. libertiana and therefore appears more regularly in localities 

 where both diseases are established. However, it appears to be more restricted in its dis- 

 tribution than »S'. libertiana, apparently on account of its failure to form mature ascospores 

 under ordinary field conditions. — Celery is attacked during the blanching process, but shows 

 considerable resistance, a 5 per cent loss being the maximum recorded. The fungus has also 

 been found on Portidaca oleracea, Verbascum blatiaria, and Sisymbrium officinale, which 

 shows that it may have numerous host plants. Inoculations of beets and carrots in winter 



