296 



" At the end of 1908 the Heveas in the nursery of the Botanic Gar- 

 dens of Surinam were attacked by a leaf-disease. The leaves took spots 

 which spread over them in concentric circles. The disease is caused 

 by a fungus living at the under side of the leaves. Only young leaver, 

 are attacked. Though the disease is a very infectious one, trees, in 

 favourable circumstances are probably little susceptible to it. The fast 

 spreading in the above mentioned case must be ascribed to various 

 accidental circumstances especially to too close planting." A figure 

 of infected leaves and the mycelium is given. Fruit does not seem 

 to have been obtained. 



The ordinary treatment for leaf fungus, either spraying with 

 weak solution of bordeaux mixture or powdering with flowers of 

 sulphur, would probably check this fungus. But prevention is better 

 than cure and as Mr. Van Hall remarks in the paper, too close plant- 

 ing is the main cause of an outbreak of this and other leaf fungi in 

 the nursery and this can and should be avoided. Make the nurseries 

 big enough and do not have each block too large. Watch for fungi 

 and presence of mites and destroy the fallen leaves which are or may 

 be affected and become sources of further infection. 



MITES. 



It is not uncommon to find in the nursery beds that many of the 

 leaves of the seedlings are irregularly twisted, bent to one side or 

 otherwise deformed; frequently one side of a leaflet is much smaller 

 than the other, and the leaflet is curved to one side. On examining 

 the underside of the leaf, it is noticeable that the tissue between the 

 nerves is swollen and the finer reticulations cannot be seen, the main 

 nerves standing out green on a greyish back-ground. With this ap- 

 pearance is associated a number of mites (acari) which live on the 

 underside of the leaves. The young ones are very minute white, and 

 elliptic and very slow in motion, the adult is larger semi-transparent, 

 with three brownish marks in the back. They do not appear to be 

 very abundant in a leaf, certainly in proportion to the alteration they 

 cause in it. The injury caused by these mites was first pointed out 

 by Mr. Arden in his report published in 1902. 



The damage seems to be practically confined to seedlings or 

 at least young plants, especially such as are weakly owing to bad soil 

 or excessive wind exposure. On well grown adult trees one rarely if 

 ever sees any injury caused or sees the presence of the mite. 

 Overcrowding in the nursery bed, a very common error, is responsible 

 for a good deal of injury to the seedlings from mites and also from 

 leaf disease. 



Frequently one sees the lowest three or four leaves attacked, and 

 spoilt, and no damage done to the next output of leaves, the mites 

 apparently disappearing. The number of mites visible is never very 

 large, but the irritation they cause to the leaf is considerable. The 



