fresh measures for the treatment of plant diseases, and many 

 of these have proved to be eminently serviceable in the past 

 ten years. Where special methods of treatment have been 

 recommended for individual cases these will be found along 

 with the diseases which are treated in the other part of this 

 work. 



Problems requiring attention. Of the problems which 

 are connected with the plant pathology of the West Indies 

 at the present time, the more important may now be 

 briefly indicated. 



The most important question, perhaps, which concerns 

 the subject of mycology in the West Indies at the present 

 time is the life-history of some of the fungi which are 

 parasitic on cacao. The more serious diseases of cacao are 

 caused by Diplodia cacaoicola, Phytophthora omnivora, 

 Nectria Bainii^ and Nectria Theobromae (along with 

 Calonectria flavida}. Of these only the life-history of 

 Phytophthora omnivora is known, that of the others remains 

 to be completed. In the case of the canker fungus, Nectria 

 Theobromae, Mr. Van Hall considers that the canker of 

 cacao in Surinam is caused by a Spicaria-form t which is 

 capable of giving rise to a Fusarium-form ; the same 

 observer regards the Nectria spp. as being saprophytic, i.e. y 

 as being incapable of affecting living parts and as being 

 only able to derive their nutriment from parts which have 

 been previously rendered lifeless. Whether this applies to 

 the canker disease in the West Indies or not, it is not 

 possible to say. A conidial form of the nature of a Spicaria 

 may reasonably be assumed to lead up to some more 

 highly developed form, and the occurrence of the Nectria 

 on the dead parts does not necessarily mean that it is a 

 saprophyte ; in fact, the perithecia of the Nectria would 

 normally be expected to occur on the dead parts of the 

 plant, after these had been killed by the mycelium in its 

 conidial phase or phases. Mr. A. Howard's investigations 

 on Nectria Theobromce in Grenada show that a form which 

 produces unicellular conidia and a Fusarmm-form are found 

 to precede the Nectria on the diseased stem. The form 

 with unicellular conidia was not, however, sufficiently 

 thoroughly described for it to be identified. The work 

 conducted in the Jodrell Laboratory at Kew has shown 

 that the product of the ascospore is a Cephalosporium-ttxm. 

 Finally, the life-history of Nectria theobromicola, a new 

 species which is parasitic on cacao in West Africa, has 

 recently been shown to be made up of a Cephalosporium- 

 form and the Nectria, The conidial form has been shown 

 to be capable of infecting the stem of the plant and of 



10 



