132 DISEASES OF CROP-PLANTS 



Vincent, where it was found fruiting abundantly on dead cacao 

 trees occurring in patches suggestive of the effects of Rosellinia 

 disease. The degree of parasitism of which this species is capable 

 requires to be established by further investigation, but on the 

 Grenada evidence the conclusion that under certain circum- 

 stances it can produce a root disease of cacao seems justified. 



As seen so far, the disease is much slower in its action than 

 that due to R. Pepo, and the failure of the trees much more 

 lingering. It is capable, however, of existing under conditions 

 of relative dryness such as appear to exclude the more familiar 

 form. 



The fruiting habits of the fungus are the same as those of the 

 species already described, and the conidial fructifications have 

 the same form. The perithecia form a dense layer on the sur- 

 face of the wood, looking like fine shot dusted thickly upon it. 



Occurrence of Rosellinia Diseases in New Clearings. 



Serious outbreaks of the diseases due to R. Pepo and R. 

 bunodes are liable to occur in clearings recently made from the 

 forest. Room for these exists at the present time, in the smaller 

 islands, only in mountain districts. The high rainfall and reduced 

 sunshine of such situations produce conditions particularly 

 favourable to the fungus, but experience in cacao plantations 

 indicates that similar troubles would be met with in new clearings 

 made at lower levels. 



The fungi concerned have not been found in a purely natural 

 habitat, i.e., in undisturbed forest, although sought for to some 

 extent. From the manner of their appearance in recent clearings 

 there can, however, be little doubt of their existence there as a 

 part of the natural flora. 



It is the usual custom in these islands, when clearings are made, 

 to burn as much as possible of the smaller material, but to leave 

 the logs on the ground to rot, and to make no attempt to remove 

 the stumps. Many of the latter send up suckers which have to be 

 cut away from time to time. Under these circumstances it 

 takes very many years before the logs and stumps finally dis- 

 appear, and during the course of their decay they make the soil 

 around them dangerously rich in crumbling woody matter and 

 humus. 



On land so prepared, as soon as the felling and burning are 

 finished, nursery plants are set out in the spaces between the 

 stumps and logs. To get anything like regularity of stand many 

 have to be placed close up to these obstacles. The writer has 

 not seen new plantations of cacao, but has had ample opportunity 

 in Dominica for examining all stages of lime cultivations thus 

 begun. 



Fungi are, of course, very abundant on the dead logs and 

 branches, but the Rosellininas are far from conunon on these or, 

 in general, on the decaying stumps. But each newly infested 



