DISEASES OF CULTIVATED PLANTS 541 



which time the symptoms are very characteristic. The foliage of 

 the affected plants takes on at the margins a mottled, metallic, blu- 

 ish-red color. The lower, outer leaves show evidence of wilt. Total 

 collapse may take place in 24 to 48 hours. Examination of the 

 stems and roots of partially matured, infected plants always re- 

 veals large, sunken lesions extending one-half to two-thirds the 

 distance through the stem or sometimes showing a sunken collar- 

 rot, so far destroying the stem as to allow the top to break off easily. 

 The experimenter has experimented upon the use of both Bordeaux 

 mixture and a straight solution of copper sulphate (bluestone) for 

 this disease upon cabbage seed beds at time of planting and upon 

 seedlings three weeks old. The formulas used were, for the Bor- 

 deaux, 4 Ibs. copper sulphate, 4 Ibs. lime, to 50 gallons of water 

 and in the straight copper sulphate solution, 4 Ibs. of copper sul- 

 phate to 50 gallons of water. (Ohio E. S. B. 228.) 



Black Rot of Cabbage. The first evidence of disease usually 

 appears in the latter part of July when the more advanced plants 

 of late cabbage are beginning to form heads. The first symptoms 

 of an outbreak are easily recognized on a hot, dry afternoon when 

 a number of the plants will appear wilted and lighter green in 

 color. A cross section of the stem of these plants near the ground 

 shows that many of the water-carrying fibro-yascular bundles are 

 black; and on splitting the stem these black lines can be followed 

 down to the withered extremity of the tap root. A diseased condi- 

 tion of any considerable number of these bundles curtails the water 

 supply and w r hen atmospheric conditions are favorable for rapid 

 evaporation from the leaves the latter quickly wilt. 



The upward movement of the water carries the disease along 

 the bundles out into the leaves. As soon as the bundles supplying 

 any considerable portion of a leaf become diseased that part of the 

 leaf dies for lack of water. The blade of the leaf becomes light 

 brown and has a texture like parchment. It is semi-transparent 

 and when closely examined the network of fine veinlets which have 

 been turned black by the disease stand out sharply in the brown 

 background. 



Early in August the disease commonly manifests itself in an- 

 other form. Brown spots appear at the margin of many of the 

 leaves, especially of those which come in contact with the soil. 

 These brown areas spread toward the center of the leaf and a close 

 examination shows the fine veins to be blackened. In from one to 

 three weeks, depending on circumstances, the disease usually 

 reaches the stem of the plant. The progress of the disease from 

 this point is identical with that brought about by infection through 

 the root. 



In either form of infection the most reliable diagnostic char- 

 acter of the disease is the blackening of the fibro-vascular bundles, 

 These bundles may be readily inspected by cutting across the leaf 

 petiole or the stem. 



The failure to supply sufficient water checks growth and often 

 results in the death of the plant. The fibro-vascular bundles do not 



