ROOT DISEASES 127 



diseases. They will probably prove to be general in their occur- 

 rence in the islands with forest areas. 



A. Rosellinia Pepo. Pat. 



This species was originally described by Patouillard in 1908 

 from material on the bark of Hymena^a Courbaril collected by 

 Duss in Guadeloupe. In the British Antilles the perithecia have 

 been collected in Dominica, St. Lucia, Grenada, and Trinidad. 

 From the published accounts of root diseases in Jamaica, Porto 

 Rico, and Martinique, it seems probable that the species also 

 occurs in those islands. 



Its most general importance is due to its attacks on cacao, 

 but it is capable ol producing destructive effects on any of the 

 ordinary crop plants, herbaceous or woody, which are planted on 

 land recently cleared from forest. Under such circumstances, 

 limes in Dominica have suffered severely from this species as well 

 as from R. bunodes. Where cacao trees have been killed by the 

 fungus, and other plants have been put in for temporary shade, 

 dasheen, banana, pigeon pea, horse bean (Canavalia) and cassava 

 have all been seen attacked. Sugar-cane seems to possess con- 

 siderable resistance, and coconut seems almost or entirely immune. 



The conidial fructifications (the Graphium stage) are developed 

 in great abundance on all kinds of dead vegetable material lying 

 about on the infested spot, and occur from an early stage on the 

 exposed roots and the base of the stem. 



They appear some time before the development of perithecia 

 and are borne on the black surface mycelium which develops 

 wherever the fungus reaches the open under damp conditions. 

 Each has the form of a black bristle-like stalk 2 to 3 mm. long, 

 built up of perpendicular hyphae which branch out freely at the 

 top into a tuft, which is white or whitish to the naked eye from 

 the conidia which cover it. The conidia are borne laterally 

 towards the terminations of these branches ; the cells which bear 

 them have a somewhat zig zag or corkscrew appearance from their 

 tendency to bend away from the point of attachment of a coni- 

 dium. The conidia are rounded or oval, one-celled, about 5 

 microns in length. 



The perithecia are borne, usually at the base of the stem, 

 amongst and in succession to the conidial fructifications, on the 

 somewhat carbonaceous layer which is formed on and in bark 

 which has become thoroughly infested. 



The perithecia are formed much less freely than in the case 

 of R. bunodes, and, in spite of long-continued search, material 

 containing ripe asci has only once been obtained in the British 

 islands ; this was found by the writer on a dead lime tree in 

 Dominica, in a situation with an annual rainfall of some 250 

 inches. Examination of this material at Kew resulted in the 

 identification of the fungus as Patouillard's species. 



The perithecia are normally slightly verrucose but are some- 



