No abstract

No abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. This content downloaded from 128.235.A bstract. The relationship between temperature and stem elongation has been investigated for representative herbaceous plants sampled from populations of seven species which were growing under semi-natural conditions in the Botanical Garden of the University of Padua (Italy). The growth of the floral stem was measured for the following species: Galanthus nii'alis L., Corydalis cai'a Schw. et Krt., Anemone nemorosa L., Symphytum tuberosuin L., Allium urs.vinum L., Aegopodium podagraria L., and Campanula rapunculoides L.Official records of daily maximum and minimum air temperatures have been elaborated by means of a new method of temperature summation. This method takes into consideration the concept that plants possess a range of sensitivity to temperature between maximum and minimum thresholds and that there is an optimal temperature for each stage of development. Data for stem elongation have been optimized (using the technique of best fit) as a function of a logistic curve which may represent growth under ideal conditions. Differences between the logistic curve and the real curve of growth may be related to the amount of deviation of values for environmental factors from optimal values. The temperature ranges between 00 C and 300 C which gave the best correlations with stem elongation have been calculated for the entire period of this process of growth. The average between the two thresholds on each day has been considered as the optimum mean temperature for that day.The optimum mean temperature increases from the start of the process to ripening, with the exception of a period just before flowering when all plants seem to require lower daily temperatures. The results of this analysis have also indicated that unknown factors other than temperature are affecting stem elongation. LITERATURE CITED

A previous investigation of fluctuations in temperature and changes in growth in seven herbaceous species under field conditions revealed a periodic lack of correlation between the two variants. An original step-by-step periodogram analysis of the curves of correlation obtained by plotting growth rate against temperature has been used in the present study. Temperature has been expressed considering the maximum and minimum daily air temperature and the upper and lower threshold values at which the temperature effect on growth is considered to be null. The growth curves, which express observed stem elongation, have been transformed to daily values of growth rate. Using a modified equation of the "logistic curve," which best fits the observed growth pattern, a theoretical representation of growth has been applied to the data. The correlation coefficient has been calculated plotting the values of temperature summation against those of growth rate for periods of 7 days. The stem growth of the seven species has revealed rhythmic components of 29.5-, 14.7-, 9.7-, and 7.3-day periods. The first two components of 29.5 and 14.7 days, which are the most evident, appear to be best correlated with the phases of the new and full moon. This fact suggests that some unknown periodic environmental change is directly or indirectly connected with the position of the moon. The other two shorter components in growth, of 9.7 and 7.3 days, may be endogenous rhythms that are expressive of the overall physiology of stem development of each species.