182 TRINIDAD AND TOBAGO BULLETIN. { XVIII 4. 



The height to which the fungus reaches is determined by the 

 moisture conditions. When the stem is well exposed it reaches no 

 further than the few inches for which the moisture of the soil can affect 

 it ; if the stem is enclosed by weeds, or low branches, or sheltered by a 

 log, it commonly goes up for a foot or more. In a case seen of a bread- 

 fruit tree growing against a bank 4 feet high, it extended upwards for 

 that distance. The limit of the external mycelium is also the limit of 

 the ultimate infestation of bark and wood. If a diseased tree is 

 up-rooted, or is cut below the limit of infestation, and thrown aside 

 where weeds grow up and shelter it, the fungus extends to tlie whole of 

 the stem and branches thu3 kept moist. 



In the rootstocks of herbaoeou.i plant <, as in tliick soft bark the firm 

 round strands of mycelium, buff-fulouied without, white within, 

 penetrate the parenchyma in all directions. 



MODE OF CONCURRENCE OF ROSELLINIA. DISEASES. 



As seen in the West Indies, the diseases due to Rosellinia, with the 

 exception of that on arrowroot, occur ; (a) on land recently cleared 

 from forest, still containing the dead and dying stumps of the 

 forest trees and retaining a considerable amount of the forest 

 humus ; (b) in cacao cultivations the conditions in which, especially 

 where shade trees are abundant, appro9ch more or less closely to those 

 of forest in respect of shade and humidity ; and (c) in wind-breaks and 

 hedges of certain susceptible trees in wet districts. The prevalence of 

 the diseases is very distinctly governed by humidity. The types due to 

 Rosellinia Pepo and Rosellinia hunodes, which alone have any consider- 

 able economic importance, are most virulent in the wet uplands of 

 Dominica, St. Lucia and Grenada; the former follows the cacoa 

 cultivations down the more sheltered valleys to the coastal districts ; 

 the latter has not been met with away from the hills. 



The Centres of the Disease. 



a. IN NEW CLEARINGS. 



The fungi concex-ned have not been found in a purely natural habitat, 

 -i.e., in undisturbed forest, although sought for to some extent. From the 

 mode 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 disap[)ear, and during the course of 

 their decay the3' malie the soil around them dangerously rich in 

 crumbling woody matter and humus. 



On land so prepared as soon as the felling and bunring are finished, 

 nursery plan'^s are set out in tiie spaces between the stumps and logs. 

 To get anything like legularity of stand many have ix> be [ila-jed close 

 up to these obstacles. 



