THE ANGULAR LEAF-SPOT OF COTTON I TYPE 317 



leaves are quite small, and then the disease is generally confined 

 to the larger veins or ribs of the leaf (Figs. 240 and 241). 



The infections are largely stomatal and are easily induced 

 by spraying on water suspensions of pure cultures (Fig. 242). 

 Two to three weeks or more, depending on the temperature, are 

 required for stomatal leaf infections to become plainly visible. 

 Their interior is then as shown in Fig. 243, i.e., the tissues are 

 disintegrating and full of bacteria. The shortest period I have 

 observed for both the vein disease and the parenchyma spot is 

 12 days. This was in very hot weather in July, 1915, using as 

 source of infection potato sub-cultures from a "windowed" 

 colony of the Arizona organism, cultivated from the leaf shown 

 in Fig. 244. 



On the green bolls which are also attacked (Fig. 245), the 

 water-soaked areas enlarge slowly or rapidly according to 

 the age of the bolls and the weather conditions. If the bolls 

 are small when attacked they drop off, and if large they become 

 first green-spotted, then brown or black-spotted and sunken in 

 the attacked parts, and the lint either fails to develop under 

 the spots or becomes wet, brown-stained and rotten (Fig. 246). 

 The pods may also become one-sided in their development. On 

 the stems, particularly the upper and softer terminal branches, 

 the elongated water-soaked spots end in long sunken black 

 stripes (Fig. 247) and the branch either shrivels and dies or is 

 broken over. The amount of branch infection varies greatly 

 according to the season and the variety. The main stem 

 of young plants is also subject to attack and may be killed. 

 From the older spots, especially on bolls and stems, there is often 

 a vellowish bacterial ooze which dries in the form of yellowish- 



*/ 



white granules, scales or crusts. 



This disease is widespread in our Southern States and has 

 been reported also from other parts of the world. I have 

 proved it to occur in Asia (Turkestan) by cultivating my 

 organism out of diseased cotton stems received from Tashkent 

 (Dr. Schroder's cotton gummosis), and with pure cultures of it 

 have reproduced the typical disease in American cotton on both 

 leaves and stems in one of our hothouses (1909). I have also 

 isolated it from stems of Egyptian cotton grown at Zomba in 



