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infections experiments could be performed. I took the precaution to 

 take a number of these pure cultivations to Grenada. The infection 

 experiments were carried out on healthy cacao pods at the Botanic 

 Station and were as follows : — 



1. On February 24th I placed some of the " roots" of the artificially 

 grown fungus into a small cavity made in the rind of a nearly ripe 

 cacao pod, taking the usual precautions to sterilise* the needles used 

 and to destroy any chance spores that might be on the outside of the 

 pod where the incision w 7 as made. Afterwards the wound was bound 

 up with a water-tight bandage. Another similar pod near was treated 

 in a similar manner, except that no fungus was placed in the cavity. 

 This served as a control or check experiment. The lesult was most 

 marked. On March 1st, i.e. 5 days afterwards, about a quaiter of the 

 surface of the pod into which the fungus had been introduced had 

 turned brown, and, on March 4th, the whole pod and its contents were 

 rotten and there was a copious development of the characteristic spore 

 sacs and spores near the point of infection. These spores agreed ex- 

 actly with that from which the artificial cultures had been made. 

 The control pod show r ed no infection. 



2. On March 11th the above experiment was repeated, and in this 

 case, two nearly ripe pods were infected with fungus from a pure cul- 

 tivation, while a third was used as a check experiment. On the 14th 

 March — three days afterwards — the two pods into which the fungus 

 had been introduced shewed very distinct infection while the check 

 experiment gave negative results. 



3. On March 4th infection experiments were made on Cacao pods 

 which were green and only about half grown in order to determine 

 whether the spread of the fungus is as rapid here as in nearly ripe 

 pods. Proceeding as above, it was found that infection with spores 

 was apparent in a week and that infection with artificially grown fun- 

 gus or with the diseased tissue from another affected pod was much 

 more rapid in the same time. The control pod showed no infection. 

 On the whole there did not appear very much difference in the rate at 

 which the disease spreads in ripe and unripe pods. In both it is ex- 

 tremely rapid. § 



4. Next an experiment was made in order to find out if the spores 

 of the fungus were able to infect a cacao pod where the rind had not 

 been wounded. On March 4th, a drop of water containing many of 

 these spores was placed on a ripe cacao pod and the drop was covered 

 with a small glass cell which was sealed into the pod by means of 

 budding wax. The cell was then covered with a bandage to shield 

 the spores from direct sunlight. On March 11th it was found that the 

 spores had germinated, but no penetration of the rind by the fungus 

 " roots" was detected. Unfortunately, it was not possible to begin a 

 further series of experiments to settle this point definitely. Although 

 this single experiment was unsuccessful, nevertheless it will be seen in 

 the following that there is every reason to believe that in the majority 



* In performing infection experiments it is necessary to be quite sure that no 

 chance fuDgus spores are introduced by means of the instruments used. It is 

 usual to ensure this by passing the needles and knives through a flame and so 

 destroy any accidental spores that may be on them. This operation is known as 

 sterilisation. 



