Plant Sanitation. 



326 



[April, 1910. 



the wood is sometimes continued in 

 narrow stripes far under the healthy 

 bark. 



How long the canker takes to kill a 

 tree I cannot say with certainty. It 

 is probable that no more than a few 

 months is required, for in July many 

 trees were found dead, which partly at 

 least had most likely only been affected 

 in the rainy season, but further obser- 

 vation on this point is necessary. 



Diseased trees may also be recog- 

 nized by their foliage becoming thinner, 

 probably when they have been diseased 

 for a long time and are slowly decay- 

 ing, while dead trees which still bear 

 their leaves probably suffered a severe 

 attack at once and were soon killed. 



All these symptoms quite correspond 

 with those of the disease known in 

 Ceylon and elsewhere as "canker," so 

 that it is doubtless the same disease 

 we have to deal with here. 



In Ceylon, the canker became wide- 

 spread in 1896, but had been occurring 

 there for some years before. Not until 

 1898 was it more carefully studied by 

 Carruthers, who in some reports re- 

 corded the results of his investigations ; 

 these were written during his investi- 

 gations and so bear a preliminary 

 character ; a more detailed account 

 has, however, never appeared, so that 

 several points, especially in respect to 

 the cause of the disease, have not been 

 fully elucidated. 



According to Carruthers it is not only 

 the stem and branches of the cacao trees 

 which are attacked, but the fruits as 

 well. In the diseased tissues he found 

 the mycelium of a fungus, and on the 

 bark the perithecia of a Nectria, which 

 he regarded as the cause of the disease 



In the West Indies the canker was 

 first noticed by Hart in Trinidad. Some 

 material of diseased trees was forwarded 

 to Massee, who detected a Nectria on it. 

 In 1901 Howard found the disease to 

 be rather common in Grenada and 

 Dominica. A Nectria and a Calonectria 

 were recorded from the affected trees, 

 According to Stockdale the canker 

 in the West Indies is now met with 

 in Trinidad, Grenada, Dominica, St- 

 Lucia and St. Vincent. In Java it is 

 also known. On one estate Zehntner 

 found the fructification of the canker- 

 fungus (probably Nectria). 



Finally in 1907 Von Faber noticed the 

 disease in the Cameroons, where, up till 

 now, it has not caused much damage. 

 Theie, also, a Nectria has been found 

 on the diseased bark. 



On microscopical examination every 

 red spot of the diseased bark appears to 

 be surrounded by a corkcambium, 

 several rows of cells thick. The colour 

 is the result of a red coloured mass in 

 the cells. The discolouration does not 

 always spread. Often a new healthy 

 tissue forms under the diseased area, in 

 which case the red bark is loosened from 

 its surroundings, dries up, becomes dull 

 brown and may easily be removed. 

 Howard noticed this in Grenada, but 

 only in rare cases and when the wood 

 had not yet been affected. Carruthers 

 often saw the moist claret-coloured tissue 

 dry up, after which it had quite the 

 appearance of dead wood. In his second 

 report he says that after having been 

 superficially shaved and exposed to the 

 air, the diseased tissue dries up and "in 

 some cases scales out and drops away, 

 while the remainder of the bark being 

 relieved from its enemy, forms a healthy 

 callus round the injury, and in course of 

 time completely covers over the shaved 

 part." Though the facts mentioned are 

 the same as those observed here in 

 Surinam, this description of Carru- 

 thers is not quite correct, for the callus 

 is formed first, and by its agency the 

 diseased patch is loosened. 



In the discoloured parts of bark and 

 wood I found the mycelium of a fungus. 

 It sometimes is very scarce, at other 

 times it is found without the least 

 difficulty. It may be especially abund- 

 ant in the youngest part of the wood- 

 Most investigators have also found the 

 mycelium outside of the discoloured 

 patches ; I have not been able to find it 

 there myself. When present in any 

 quantity Carruthers saw the mycelium 

 running in the wood as thin black 

 strands. Like v, Faber, I am unable to 

 confirm this statement. 



In order to make a closer study of the 

 fungus it had to be grown artificially. 

 With a sterile knife small pieces were 

 cut from the wood at the borders of the 

 diseased and the healthy tissues. These 

 were transferred to a culture-medium in 

 a sterilized dish. In a few days the 

 mycelium came forth from these pieces 

 as a pure culture. In this way the 

 parasite could always be easily obtained. 

 Soon a conidial fructification developed ; 

 on a septate mycelium appear branched 

 conichophores, from which oval uni- 

 cellular eonidia are cut off. 



I consider the fungus as belonging to 

 the genus Spicaria. Very characteristic 

 of this Spicaria is its property of impart- 

 ing a red colour to some culture-media. 



In the course of my investigations I 

 found another fructification in a two- 



