DISEASES OF PLANTS 61 



It must be admitted that Gerretsen has made a strong case 

 for the view that grey speck disease is not the result of man- 

 ganese deficiency only. The problem is clearly deserving of 

 further study. 



In wheat, Gallagher and Walsh (1943) observed that the first 

 sign of manganese deficiency usually appears with the develop- 

 ment of the third or fourth leaf. Frequently there is a general 

 similarity with grey speck of oats, but the transverse line of 

 withering tends to occur nearer the tip of the leaf than in 

 oats, later extending to the lower regions of the leaf. The 

 withering may develop as in oats by the coalescence of small 

 grey elongated areas or it may begin at the leaf margin. As 

 soon as the line of withering reaches right across the leaf the 

 upper part of the leaf soon loses its green colour. Sometimes, 

 instead of the development of the line of withering across the 

 leaf as in oats, small grey oblong areas appear scattered parallel 

 with the veins. The whole plant becomes chlorotic and the leaves 

 wither, beginning at the tip. 



In barley, Gallagher and Walsh record the first symptom of 

 manganese deficiency to be a localized paling of the leaf, followed 

 by the development in a few days of small grey oblong spots with 

 brownish margins. These enlarge and coalesce to form stripes 

 parallel with the veins. Sometimes the spotting is most marked 

 near the tip, which finally withers. The plant as a whole becomes 

 somewhat chlorotic. 



Rye appears to be affected by manganese deficiency in much 

 the same way as oats, the spots that develop on the leaves being 

 described by Gallagher and Walsh as whitish. The leaves bend 

 over in the same manner as those of oats affected by grey speck. 

 Neither barley nor rye, however, appears to be so badly affected 

 by manganese deficiency as oats. 



From the work of Pettinger, Henderson and Wingard (1932), 

 manganese deficiency appears to produce a chlorotic condition 

 in maize very similar to grey stripe. In sand-culture experi- 

 ments with maize they met with three types of chlorosis which 

 they attributed respectively to deficiency of magnesium 

 (type A), excess of sodium (type B) and deficiency of manganese 

 (type C). In type A the chlorotic areas take the form of long 

 narrow streaks more or less continuous from the base to the 



