236 PLANT GROWTH SUBSTANCES 



beginning of the present century the plants grew well anywhere in the 

 coastal lands. In 19 10 a wilt was reported which started to invade 

 plantations especially in the moist areas with acid soils. By 1920 this 

 wilt, caused by Fusarium oxysporum cubense, had become a major prob- 

 lem which finally drove the industry from the original plantations (32). 

 Thus, new jungle had to be cleared for new banana plantations and new 

 crops had to be found to occupy the abandoned banana lands. Cacao 

 proved to be one of several crops suitable for replanting the old banana 

 lands. In order to make culture profitable it is necessary that the planta- 

 tions consist of trees which combine a high yield of high quality fruit 

 with a reasonable resistance against diseases. This is only practical at 

 present by the vegetative propagation of parent plants of proven out- 

 standing performance in these respects. In cacao this propagation is 

 done most profitably by cuttings, which brings us back to our starting 

 point. 



When cuttings are taken from a cacao tree without any special pre- 

 cautions, and then planted in a propagator, they will wilt and fail to 

 form roots. The reason for this is that the bark of the cacao tree contains 

 mucoid material. When the cutting is taken from the branch this will 

 ooze out and plug the xylem vessels, thus causing the death of the cutting 

 by water starvation. When the cut stem ends are kept in water before 

 being transferred to the propagator much of this trouble can be avoided. 

 This is an example of how a seemingly minute detail may spell success 

 or failure of a technical process. 



There are many other conditions which have to be observed for the 

 successful rooting of cacao cuttings (8,9,18). Without auxin treatment, 

 however, root formation will still be unsatisfactory. When, however, 

 cuttings are treated with a suitable auxin prior to being placed in the 

 propagator, the following benefits result: roots are formed faster; a larger 

 percentage of the cuttings forms roots in a shorter time; and the cuttings 

 are more easily transplanted because under auxin treatment a compact 

 root system composed of many short roots results. These are the reasons 

 that synthetic plant hormones have become an integral part of propaga- 

 tion by means of cuttings. 



The most widely used of the synthetic auxins for this purpose is 

 indolebutyric acid (IB). It is used either alone or in combination with 

 other auxins such as NAA (24). In practice it is most frequently formu- 

 lated as a powder. The moistened ends of the cuttings are dipped into 



