摘要:

SUMMARY1Previous investigations on the pollination of cacao are reviewed. It is pointed out that the consensus of opinion is in favour of the pollinating agent being small insects, either thrips, aphides or ants.2Direct proof of natural crossing was obtained by examination of flowers on a male sterile tree, in which 9 per cent. of the flowers were found to be pollinated.3Daily examination of flowers artificially pollinated, flowers attended by ants and aphides, and flowers with no attendant insects, indicated that the majority of cacao flowers are never pollinated under Trinidad conditions. Adequate pollination took place in 35 per cent. of flowers attended by ants and aphides, and is only 6 per cent of the controls. It is concluded that ants and aphides are the chief pollinating agents in the field under examination.4Elimination of crawling insects demonstrated the presence of another pollinating agent, probably a night flying insect which pollinated about 1 per cent. of flowers.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1925.tb04236.x

出版商:Blackwell Publishing Ltd    

年代:1925

数据来源: WILEY

摘要:

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.1In 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.2Secondly 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.3The third point of interest is the sex‐ratio.The sex‐ratios of the individualtrees 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 thesex‐ratio of the population showsa 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

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1925.tb04237.x

出版商:Blackwell Publishing Ltd    

年代:1925

数据来源: WILEY

摘要:

SUMMARYIn the absence of transmission of streak disease by the seed, the wide occurrence of this disease in maize in South Africa is accounted for by infection of the plants at some period after their appearance above ground. It has been shown that plants may be protected from infection by growing them in a greenhouse or under wire‐gauze of not less than 32 meshes to the inch.A number of insects have been tested as possible vectors of streak disease, and positive results have been obtained with a jassid,Balclutha mbilaNaude. In four cases out of five, to each of which were introduced three or four adults of this species, collected on streak‐diseased maize, the disease developed in every plant. The plants hi three similar cages, to which no jassids were introduced, remained healthy.In experiments in which single individuals ofBalclutha mbila, collected upon streak‐diseased maize, were allowed to feed upon single leaves of the experimental plants, the disease resulted in 46 out of 48 plants. One jassid lived for five months and carried the disease to eight separate plants. No loss of the power of infection occurred in any jassid tested, in spite of periods of starvation in some cases or of feeding on apparently immune plants in others. Certain individuals, collected upon streaked maize were incapable of causing any infection under similar conditions.Jassids reared upon healthy maize were incapable of infecting plants with streak disease. But after feeding upon a diseased leaf for a week, 26 per cent. of the males and 86 per cent of the females, out of a total of 62 individuals, became infective.Negative results were obtained in trials ofAphis maidisFitch,Peregrinus maidisAshmead and a number of undetermined jassids and fulgorids.Field observations showed thatBalclutha mbilawas to be found, although infrequently, whenever a field of maize, recently infected with streak disease, was thoroughly searched. It is held therefore to be the agent of spread of the disease in the

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1925.tb04238.x

出版商:Blackwell Publishing Ltd    

年代:1925

数据来源: WILEY

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1925.tb04239.x

出版商:Blackwell Publishing Ltd    

年代:1925

数据来源: WILEY

摘要:

SUMMARY1A technique has been developed, whereby the influence of various factors such as temperature, manurial treatment, soil conditions, age and variety of the plant on the infestation of beans byAphis rumiciscan be tested.2Factors which influence the physiological activity of the plant, thereby affecting growth and the nature of the cell sap, affect also, through the food factor, the progress of the aphis infestation.3Experiments have been carried out during four years, the methods employed being fully described. The chief features of the technique are: (a) The same strain of aphis was used throughout and infestations were made with sisters of the same generation for all comparable series. (b) The same variety of beans was used throughout and with comparable series the plants were always of the same age. (c) The reproduction period in all comparable series extended approximately over the same days, so that temperature and other climatic factors were the same for all the series.4The experiments were in series, each series consisting of five plants, each plant being infected with one a.v. female. The aphids present on each plant at the end of a definite reproduction period were counted and the mean of the counts for the five plants was taken as the mean infestation figure for the series concerned.5Temperature influences the developmental period of the aphids and also the daily production of young, thereby affecting the infestation figures, so that the reproduction period for all comparable series was taken during the same days.6Significant differences in infestation have been obtained with certain series, these differences being considered as indicating differences in the feeding value of the plants in the different series.7Beana grown in soil treated with complete mineral manures became slightly more heavily infested than those grown in unmanured soil. In unmanured sand low infestation figures were obtained.8Beans grown in sand watered with normal culture solution gave higher infestation figures than those grown in soil watered with the same solution.9Beans supplied with increased potash indicated increased infestation figures, whereas with low potash a decrease was obtained.10Beans grown in sand watered with culture solution containing increased MgSO4showed a marked increase in infestation.11Experiments repeated for three years, in which varying amounts of daylight were available for the plants, show that with reduction of the light, a decrease in infestation is obtained. Similarly in Winter when artificial light, in excess of the ordinary daylight, was used, an increase in infestation was obtained compared with those plants which only received daylight. This is probably associated with the carbohydrate content of the plant sap and the decrease in young growth.12Bean plants six weeks older than the controls gave a marked decrease in infestation figures.13Beans grown in acid soil and in badly aerated soil conditions, did not show any difference in infestation, compared with the control series, but owing to the low temperature during the reproduction period the results are inconclusive.14The relation between the optimum temperature for the growth of the host plant and that for the development and reproduction of the aphids is an important consideration with reference to outbreaks of aphis infestation.15The results obtained in these experiments show that aphids react to physiological changes in the host plant. They problems have a wide application to plant‐sucking insects in general, but the experiments only represent a preliminary investigation of a wide and important subjec

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1925.tb04240.x

出版商:Blackwell Publishing Ltd    

年代:1925

数据来源: WILEY

摘要:

SUMMARYDuring the year 1924 additional data, in relation to varietal resistance to attack, were collected by repeating as nearly as possible the investigation conducted during the previous year, with the exception that only those varieties of oat were used, which were most (GoldfinderandNew Abundance) and least resistant (SuperbandSupreme).During the second season, during which, on the whole, conditions were unfavourable to damage by frit fly, varietal differences were again effective so far as stem infestation was concerned. The two varieties,GoldfinderandNew Abundance, were significantly resistant as compared with the varietySupreme, similar differences being observed in the two seasons. Very late sowing indicated that varietal differences among very young plants were ineffective in influencing extent of infestation.Small significant differences were observed in relation to the grain infestation, but from the evidence available it would appear that constant values for these differences are unlikely to occur over a period of years, because extent of infestation is largely dependent on the history of the crop during the early growing period.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1925.tb04241.x

出版商:Blackwell Publishing Ltd    

年代:1925

数据来源: WILEY

摘要:

SUMMARYOat plants, of known stage of growth, were exposed to Frit Fly attack at different growth periods, with the result that the susceptibility of the main stem to attack was found to be most marked during the two‐ and three‐leaf stages of growth. In the four‐leaf stage susceptibility decreased and beyond this stage the shoot seemed to be immune relatively. Plants in the early one‐leaf stage showed a certain degree of immunity, due probably to size non‐attractiveness rather than to specific morphological characters.Considered in conjunction with the constancy of the prevalence periods of the fly, these observations have a certain importance. Thus a practical solution of the Frit Fly problem may be found either by early sowing (as is already well known) or by the selection of a variety which passes rapidly through all stages of growth preceding that described as the “four‐leaved.” The next step in the investigation would appear to be an examination of the different races or varieties of oat, in order to compare their rates of growth up to and inclu

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1925.tb04242.x

出版商:Blackwell Publishing Ltd    

年代:1925

数据来源: WILEY

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1925.tb04243.x

出版商:Blackwell Publishing Ltd    

年代:1925

数据来源: WILEY

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1925.tb04244.x

出版商:Blackwell Publishing Ltd    

年代:1925

数据来源: WILEY

摘要:

SUMMARY1Under the name “Nettlehead” two quite distinct diseases, “true” and “false,” have been noticed.2In the case of “False” Nettlehead the bine usually dies away in August and the root system is in a state of decay; in the “True” form the bine remains green though growth is retarded, at the same time the root system remains in an apparently healthy state.3The “True” form is usually to be found starting from the edge of a garden especially where the garden slopes down to a deep ditch or high hedge. “Fahe” Nettlehead, on the other hand, may be found distributed throughout the garden.4The Beet eelworm,Heterodera Schachtii, may be found in all hop gardens, but its presence is not correlated with “Nettlehead.”5“True” Nettlehead has been in greater evidence the y

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1925.tb04245.x

出版商:Blackwell Publishing Ltd    

年代:1925

数据来源: WILEY