Annals of Botany Volume 19 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1905 Excerpt: ... the way that is indicated by other experiments. Extending the schema that we have arrived at to higher temperatures than 40-5 C, we find at 450 C. a still more rapid fall of the assimilation, for which, however, we have no suitable numerical data, and this declines to zero in a comparatively short time. This is represented in the diagram by the curve starting from F. Finally, to conclude the series we ought to find a temperature at which the earliest estimation that could be actually made would give no measurable assimilation. The lowest temperature to give this result might be called the 'extinction temperature, ' and here we should hypothecate that, for the first few seconds after attaining it, each chloroplast would give a higher assimilation rate than at any lower temperature, but that the rate would immediately fall, and that so rapidly that it would become nil almost at once (say in 100 seconds, for the accepted specific extinction temperature would of course have to be arbitrarily defined in time-units). In estimating carbon-assimilation in the presence of over-balancing respiration, it is almost impossible that this temperature should be determined directly, but we are accumulating evidence as to the location of it. I have placed it at 480 C. in the diagram. We thus arrive at a complete theoretical schema of the primary relation between the rate of the photosynthetic process, different temperatures, and time. Now, without going into details again, it may be stated that for cherrylaurel leaves the process of respiration, although it contrasts powerfully with assimilation as to its metabolic significance, also shows quite the same kind of relation to temperature. I therefore venture to suggest that, making suitable changes in the coefficients of tempe..