10 BULLETIN 829, U. S. DEPARTMENT OF AGRICULTURE. 



limiting their extent or direction except that in general they are 

 elongated in the direction of the parallel veins of the leaf. 



In D 95 the light areas are predominant from the start (PL I, fig. 5) . 



In L 219 the light streaks are isolated near the base of the leaf but 

 become confluent toward the tip. 



In L 226 the streaks are isolated and even in older leaves remain so. 



L 231 is very severely injured. The leaves are usually quite yellow, 

 as shown in Plate I, fig. 6. Practically the entire surface is light 

 from the beginning. There are exceptions, however. The amount of 

 injury in this variety is variable. 



L 253 is quite tolerant. The lighter areas predominate but are not 

 yellowish. All plants seen were dark green and vigorous. 



SECONDARY SYMPTOMS. 



Field observations covering a number of }'ears indicate that the 

 deleterious effects of the mosaic disease are cumulative. The streak- 

 ing and spotting of the leaves discussed above are the only noticeable 

 sign in newly infected plants. The disease is never fatal during the 

 first year and, in fact, it rarely terminates in death even in diseased 

 plants that have been allowed -to ratoon for years. Usually, however, 

 more serious effects are seen in first ratoons of cane which became in- 

 fected the previous year or in plant cane originating from diseased 

 cuttings. At this time another quite distinct leaf symptom appears. 

 It consists of small white opaque spots and streaks in the light-colored 

 areas. These streaks are smaller than the light areas previously men- 

 tioned and differ from them in having no pigment whatever. They 

 range from mere points to elongated irregular streaks several inches 

 in length. The white streaks may become confluent to a limited 

 extent. They are for the most part restricted to the light-green areas 

 of affected leaves, but do not correspond to them in outline and 

 typically remain more or less isolated from one another. The white 

 opaque tissue has a dried-out appearance and seems to be quite 

 functionless. It remains firm, however, and does not become brown 

 or rot out. The amount of total leaf area occupied by this type 

 of tissue rarely exceeds 20 to 30 per cent of the whole. 



At about the same time, or during the next year, a still more in- 

 jurious sign of mosaic appears, namely, the striping or cankering of 

 the stalk. This is much more marked in some varieties than in 

 others. Ordinarily, it does not become noticeable until the cane is 

 quite well developed. By tearing away the enveloping leaf bases, 

 cankers can sometimes be found in the incipient stage. They appear 

 as discolored or water-soaked patches or longitudinal streaks on the 

 internodes. In severe cases these areas become sunken and the 

 internodes are spindle shaped and attenuated. Longitudinal cracks 

 may appear, resulting in the drying out of the cane.- There is a 

 tendency toward shortening of the joints and premature development 



