GROWTH AND CORRELATION IN THE OIL‐PALM (ELAEIS GUINEENSIS)

Abstract

SUMMARYThe work reported in this paper constitutes a first attempt to study the growth processes in a tropical palm. Three points of primary interest have come to light in the course of the investigation. In the first place it has been found that young trees have two flowering cycles in the course of the year, one in the autumn and the other in the spring. The modes of the flowering cycles correspond closely to the two periods of equal day and night. The correspondence is remarkable in view of the latitude of Ibadan, viz. 7° 22′ 30“. The suggestion was made that two distinct groups of environmental factors control the seasonal flowering cycles. The first group determines the laying down of the inflorescence primordia and is doubtless identical with that affecting leaf production. The annual distribution of rainfall is unquestionably the most important factor in this group. The second group of factors is active in promoting the actual flowering of the inflorescences. It is suggested that the relative length of day and night is a factor of paramount importance here. Secondly it has been ascertained that as trees age, there is a tendency for the spring flowering cycle to be eliminated. The suppression of the spring cycle seems to be correlated with an increase in the weight of the individual bunches. This correlation only obtains until the trees are 30–40 feet in height, after which senescence is probably a factor in the economy of the palm. It is suggested that the increasing weight of the individual bunches leads to the exhaustion of food reserves. The strain of maturing the fruits that develop from the autumn flowering cycle must be considerable, for the growth of these fruits takes place in the dry season. It is considered that this exhaustion of the plant's reserves may be responsible for a shortage of female spadices during the spring period of equal day and night. The third point of interest is the sex‐ratio. The sex‐ratios of the individual trees were found to vary greatly. Some trees were completely male throughout 1924, but none were completely female. A few trees produce a large proportion of bisexual spadices. It was noticed that there was a slight tendency on the part of individuals that were especially active in the production of leaves to have a relatively high proportion of female spadices. It seems probable that though genetic factors are of chief importance in determining the differences observed in the sex‐ratios, yet the influence of the individual's environment is by no means negligible. It would appear that the relative sex‐ratios of the trees do not fluctuate very markedly from year to year, for the correlation coefficient between the sex‐ratios of the trees in 1924 and number of bunches produced in the preceding two years amounts to ‐ 0·40 ±·065. It is therefore concluded that the sex‐ratio is an important factor in determining the yield of bunches of fruits; relatively female trees tend to produce a large number. It has been found that the sex‐ratio of the population shows a somewhat regular seasonal periodicity. Almost invariably there is an excess of male inflorescences, but this excess becomes particularly accentuated in December. Our data do not permit us to judge to what extent the December excess of males is due to a relatively greater mortality of young female spadices at this time, and to what extent it is due to a true periodicity in the differentiation of sex. It was observed that there was a larger proportion of female spadices in the autumn cycle of 1923 than in that of 1924. Again we are unable to decide to what extent this was due to differences in climate in the two years and to what extent to the age of the trees.In conclusion we have pleasure in acknowledging our indebtedness to the Surveyor‐General, Nigeria, for his courtesy in supplying us with particulars of the relative length of day and night at Ibadan.