170 DISEASES OF CROP-PLANTS 



of what he regarded as a fungus of the type associated with 

 some forms of witches-brooms in Europe and described it as 

 Exoascus TheohromcB. Massee did not find this fungus present, 

 and Howard observed only Fusarium spores. Went was the 

 first mycologist to see fresh material. He found a mycelium 

 in the tissues which did not fruit in cultures or reproduce the 

 disease from inoculations. Van Hall and Drost (1907) made an 

 elaborate study of the disease and concluded that it was due 

 to CoUetotrichum luxificum, which appears abundantly on the 

 affected shoots and indurated pods ; inoculations failed. 



Rorer (1913) pointed out that C. luxificum is common in 

 Trinidad although the disease is absent, and, further, that the 

 mycelium in the affected shoots has clamp-connections which are 

 characteristic of the Basidiomycetes. Inoculations with the 

 mycelium were unsuccessful. 



G. Stahel (1915) confirmed Rorer's findings, and examining 

 the old witch-brooms for fructifications, found those of a Maras- 

 mius commonly present. The spores from this fungus allowed 

 to fall on buds enclosed in test-tubes gave rise to the disease in 

 {a) 14 out of 46, {h) 7 out of 9, (c) 9 out of 10 cases, and infections 

 were produced on a plantation previously free from the disease. 

 Mycelium in pure cultures from the Marasmius spores agrees 

 with that found in the shoots. The indurated pods contain 

 an exactly similar mycelium and also bear the Marasmius fructi- 

 fications, and both these and the diseased cushions have been 

 readily produced by infection with Marasmius spores. 



Nature of the Disease. 



Van Hall and Drost's description of the appearance of a 

 hypertrophied twig (witch-broom or krulloot) is as follows 

 (Fredholm's translation) : " It is generally two to six times as 

 thick as a healthy twig, its surface is rough and somewhat 

 furrowed, its base turgid, at times exhibiting longitudinal cor- 

 rugations. The leaves do not become fully developed, but 

 remain soft and flimsy like recently unfolded leaves on sound 

 twigs ; often they are of a darker colour. Among other char- 

 acteristics should be mentioned the bending over of axillary 

 buds, even before the witches-brooms are fully developed, 

 the strong tendency to produce side-shoots, the retention of the 

 supporting leaves, the growth of the shoots in a vertical direction 

 and their short duration." 



The shoot never becomes woody ; it grows quickly, and in 

 three to six weeks it dries up from the base. Both axillary and 

 terminal buds and flowering shoots are liable to the affection. 

 The bud infection does not in all cases involve the growing 

 point, in which event the top of the shoot may develop normally. 



The indurated pods, which always occur in association with 

 witch-brooms, are of three types : (i) in which the principal 

 symptom is the hypertrophy of the stalk — these arise from 



