Aprii, 1910.] 



329 



Plant Sanitation, 



In my opinion he is not entitled to 

 this conclusion for the following rea- 

 sons. The symptoms of the disease on 

 pods, as was also noted by v. Faber, 

 correspond closely to those caused by 

 Phytophtora; besides, according to Petch 

 the Nectria in cacao pods in Ceylon is 

 not the same as that on the stem. He 

 says : " If the stem and pod-diseases 

 are the same, they cannot be due to 

 Nectria." 



Nor is it proved by the observations 

 made in other countries, Howard does 

 not mention a Nectria on pods, except 

 the one found by Hart in Trinidad and 

 described by Massee as Nectria Bainii, 

 and the pod disease on Ceylon which 

 after Carruthers' reports may be caused 

 by Nectria or one of the Peronosporece, 

 or by both. Nearly all pods, forwarded 

 to Kew on that occasion, appeared to 

 be attacked by Phytophtora. 



Zehntner speaks of "the rare cases 

 where a canker patch appears at the 

 junction of a pod with the stem and 

 the canker fungus spreads along the 

 stalk to the pod itself." In the Came- 

 roons v. Faber never observed an in- 

 fection of pods by Nectria. Here in 

 Surinam I have never found a Nectria 

 as a cause of disease in pods, neither 

 have I seen the canker fungus (Spicaria- 

 Fusarium) as a parasite on pods. 



From this survey it is evident that 

 Carruthers' infection experiments and 

 the few observations of Zehntner are 

 the only foundations for the belief that 

 canker is a pod-disease ; on the con- 

 trary, everything seems to show that 

 Carruthers was concerned with the 

 " black rot " (blackening of pods), due 

 to Phytophtora, which is known to 

 attack pods in Ceylon, Java, the West 

 Indies, the Cameroons and Surinam, 

 and to cause a great deal of damage 

 in all these countries, except in Java. 

 Petch asserts that in cases where the 

 disease had spread from pod to stem, 

 in sterile chambers Phytophtora de- 

 veloped from pieces of bark, peduncle 

 and pod ; if this statement should prove 

 to be correct, it would show that 

 Phytophtora can attack the stem as 

 well as the pods. 



Barrett attributes to one and the same 

 fungus (Laaiodiplodia) the " brown rot" 

 of the pods and the canker (red rot) 

 of the stem (as appears from the des- 

 cription of the symptoms). This state- 

 ment can hardly be correct ; it is true, 

 that Lasiodiplodia (most probably iden- 

 tical with Howard's Diplodia and per- 

 haps with v. Hall's Chaetodiplodia) does 

 cause the "brown rot" of the pods 

 and also a stem-disease ; but this stem- 

 disease is the so-called "die-back," 

 42 



which is quite different from the 

 Ceylon canker, induced by S'picaria- 

 Fusarium. I mention this because this 

 mistake may give rise to confusion. 

 For the same reason Barrett's use of 

 the term " canker in its broad sense to 

 include the destruction of woody tissues 

 by any parasitic fungus," is not to be 

 recommended, now that the name can- 

 ker has already been given to a defi- 

 nite disease. 



Carruthers not only tried to combat 

 the disease by treatment cf affected 

 trees, but also by removing the con- 

 ditions which assist in spreading it. 

 As he regarded dampness of the atmo- 

 sphere as the most dangerous factor on 

 account of the favourable conditions it 

 offers to the fungus, he urged before 

 all things the necessity of removing 

 superfluous shade and of draiuing the 

 soil, especially in low hollows. Besides 

 this, he advised the planters to burn 

 the dead trees and to bury or burn all 

 discoloured pods in order to destroy the 

 infection-material. As suckers were 

 scarcely ever affected, he recommended 

 not to cut them all in the usual way. 



The direct treatment of the trees was 

 to consist in the excising of the dis- 

 colouied patches with a large margin of 

 the surrounding tissues as the fungus 

 mycelium had been found outside the 

 discolouration, or, if the spots were too 

 large, in superficially shaving them and 

 exposing the parts so treated to the dry- 

 ing effect of the sun. All excised parts 

 were to be burnt. 



Meanwhile, Wright had made the ex- 

 periment of ppraying the pods with a 

 mixture of sulphate of copper and lime. 

 As it is however highly probable (as 

 has already been pointed out), that 

 the disease of the pods is not canker, 

 but caused by Phytophtora, his favour- 

 able xesults do not teach us anything 

 about the treatment of canker, how- 

 ever important they may be in other 

 directions. 



In Java and the West Indies Carru- 

 thers' advice is also followed. In the 

 West Indies the wounds are, in addition, 

 treated with tar, as Nectria is a wound 

 parasite and the spores should not be 

 given an opportunity of penetrating 

 into the tissues. Carruthers disagreed 

 with the application of tar. as it might 

 prevent the control of the excised spots. 



In the West Indies the number of 

 canker cases has also diminished, al- 

 though the disease has not been eradi- 

 cated. 



In Surinam canker patches are 

 generally excised ; after this the wound 

 is left uncovered for some days to 



