58 DISEASES OF CROP-PLANTS 



foliage of the infested tree. The combined effect is to produce a 

 sickly ill-nourished condition in the host and frequently the death 

 of the terminal parts of infested branches. 



By analogy with the European species it is assumed that the 

 distribution of the local mistletoes mainly depends on birds, 

 which feed upon the berries and leave the sticky undigested 

 seeds adhering to the bark of trees subsequently visited. The 

 primary root produced in germination penetrates the cortex 

 as far as the wood, where it spreads out into an ultimately woody 

 organ of attachment. The wood of the host is not actually 

 penetrated, but the base of the organ becomes more deeply 

 buried every year by the addition of the annual rings of wood 

 to the branch, with which the parasite keeps pace by step-like 

 or finger-like extensions. 



When its first appearance is neglected, bird-vine may become 

 a serious pest of cacao and of limes, to mention the two most 

 important of its hosts. The species Dendropcmon caribceus 

 Krug. et Urb. is very abundant in semi-neglected lime fields in 

 Dominica. Another species is reported to be common on avocado 

 in the Virgin Islands. 



Of the numerous species occurring in Trinidad, by far the 

 worst pest of economic plants is Struthanthus dichotrianthiis 

 Eichl, which attacks cacao, mango, orange and many other trees. 

 It is peculiar in the possession of aerial roots which run along the 

 branches of the host and rapidly extend the infestation. 



The only remedy for mistletoe is cutting out and pruning, 

 carried out in the course of systematic inspections. The cleaning- 

 up of infested trees throughout a district is desirable, and legisla- 

 tive action to secure this has been taken in Trinidad and St. Lucia. 



An insect, not identified, has been reported to destroy the 

 berries of the Dominica species above mentioned. 



Alectra : Cane Killer. 



In 1892 C. A. Barber described the occurrence of a Scrophu- 

 lariaceous parasite reported to be destructive on sugar-cane 

 ratoons in Dominica. The species was Alectra brasiliensis, 

 Benth., which is recorded as also occurring in Guadeloupe, St. 

 Vincent and Trinidad. The plant is erect, unbranched, one to 

 three feet high, with opposite, toothed green leaves, about an 

 inch long, arranged closely on the stem. The flowers occur in the 

 axils of the leaves, are yellow and inconspicuous, and may be 

 recognised by the curved stigma which appears like a broad 

 green band across the throat of the corolla. Immense numbers 

 of minute rod-shaped seeds are produced in the capsules. 



The parasitism is partial only, consisting of the attachment 

 of the roots (which are orange coloured) to those of sugar-cane or 

 other plants. It is only effective on old ratoons, and apparently 

 does not occur where tillage is adequate. Nothing has been heard 

 of its existence as a pest in recent years. 



