Photosynthesis in Water Plants

24I Dichtyuchus, and Aplanes in form, manner of discharge, and germination of spores.A common type of variation is one in which chains of rounded sporangia discharging laterally are formed.It is well to have these variations recorded from observations on a single form in pure cultures.-H.HASSEL- BRING.Photosynthesis in water plants.-BLACKMANand SMITH20 have published two papers upon "Gaseous exchanges of submerged plants," being nos.8 and 9 of the excellent series on "Experimental researches on vegetable assimilation and respiration" issued from BLACKMAN'S laboratory.The first of the present papers deals with "A new method for estimating the gaseous exchange in submerged plants."Instead of using the oxygen elimination as the basis for study, the CO2 consumed is determined.Water of known C02 content (determined by tritation) is passed over submerged plants of a given illuminated surface, and the CO2 withdrawn for photosynthesis determined by later titration.Correction is made for CO2 produced by respiration and for that in the eliminated gas.The method seems to insure reasonable accuracy.In agreement with other workers, BLACKMAN and SMIT H find Elodea extremely sensitive to adverse conditions.A few days of storage in tap water in laboratory or greenhouse cuts the assimilation I7 to 30 per cent.The plant also endures great concentration of CO2.Water saturated from an atmosphere containing 30 per cent CO2 does not interfere with assimilation; it is not likely that air plants would long endure such concentrations.The points of large significance can be set forth by quotations from the summary of the second paper: "The aim of this study is to demonstrate the nature of the relation between assimilation and the chief environmental factors: (i) C02-supply, (2) lightintensity, and (3) temperature.The relation is such that the magnitude of this function in every combination of these factors is determined by one or the other acting as a limiting factor.""The identification of the particular limiting factor in any definite case is carried out by applying experimentally the following general principle.When the magnitude of a function is limited by one of a set of possible factors, increase of that factor, and of that one alone, will be found to bring about an increase of the magnitude of the function.""The experiments in this paper deal with such moderate intensities of assimilation as may be fairly well maintained for several successive hours.WVith more intense assimilation the values soon fall off by the action of internal factors grouped at present as the time factor.Experiments in which this additional factor has to be reckoned with will be considered in a later paper."