DISEASES OF COCONUT i8i 



occurring up to ten years are not particularly rare and odd cases 

 have been verified in trees over twenty years old. 



Examples of the disease have been seen by the writer in all 

 grades of soil, from beach sand and rich vegetable mould to 

 exceedingly stiff clay. No influence on liability to the disease 

 has been detected as proceeding from these variations or from 

 any unfavourable conditions of growth. 



A very large number of cases have occurred in certain planta- 

 tions on virgin soil cleared from forest, and infestations as severe 

 are found on land which from a remote period has been cultivated 

 in sugar-cane. On the other hand, one large estate in Trinidad 

 converted from sugar-cane to coconuts ten to fifteen years ago has 

 so far not had a single case. 



Mode of Infection. 



Information as to the beginning of the disease is as yet scanty 

 and uncertain. The rapidity of infestation shown in the infection 

 experiments renders untenable the hypothesis first put forward 

 that infection takes place at an early age without its effects 

 becoming outwardly visible until the tree matures. Subj ect to the 

 results of further investigation, it may be said that infection 

 probably takes place at the base of the leaves. The dorsal 

 connection which is very regularly visible between the infestation 

 in a leaf base and the external natural fold which is formed near 

 its junction with the stem suggests that the cracks which occur 

 in this situation may provide an opening for infection. 



It is considered probable that the worms ascend from the soil 

 by way of the surface of the stems and gain entrance at the base 

 of the leaves. This is known to occur in nematode diseases 

 of rice and black currant. (See Chapter V.) 



The location of the red zone in the stem cannot yet be ex- 

 plained. Its position is the same in trees artificially infected 

 by way of the leaves or through holes bored in the stem. 



The Parasite. 



From material supplied by the writer the worm has been 

 described by N. A. Cobb as a previously unknown species, and 

 named Aphelenchus cocophilus. The length of the adults, 

 male and female, is i mm. (oV inch). The eggs, which are cylin- 

 drical and slightly curved, are deposited in the living tissue. 

 Nothing is known as to the existence of the worm outside of the 

 tree 



Control. 



Until the process of infection becomes more certainly known, 

 advice given regarding control measures must be largely con- 

 jectural. The manner in which the disease spreads in lines and 

 groups from the scattered cases which first arise is conclusive 



