Tori] f CURRENT LITERATURE 241 
Dichtyuchus, and Aplanes in form, manner of discharge, and germination of 
spores. A common type of variation is one in which chains of rounded spo- 
rangia discharging laterally are formed. It is well to have these variations 
recorded from observations on a single form in pure cultures—H. Hasset- 
BRING : 
Photosynthesis in water plants.—BLAcKMAN and SmirH” 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’Ss 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 CO, consumed is determined. Water of known CO, content 
(determined by tritation) is passed over submerged plants of a given illumi- 
nated surface, and the CO, withdrawn for photosynthesis determined by later 
titration. Correction is made for CO. produced by respiration and for that 
in the eliminated gas. The method seems to insure reasonable accuracy. 
In agreement with other workers, BLACKMAN and SmitH find Elodea 
extremely sensitive to adverse conditions. A few days of storage in tap 
water in laboratory or greenhouse cuts the assimilation 17 to 30 per cent. 
The plant also endures great concentration of CO,. Water saturated from an 
atmosphere containing 30 per cent CO, 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 mature of the relation between 
assimilation and the chief environmental factors: (1) CO,-supply, (2) light- 
intensity, and (3) temperature. The relation is such that the magnitude 
of this function in every combination o 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.’ 
e experiments in this paper deal with such moderate intensities of 
assimilation as may be fairly well maintained for several successive hours. 
- With 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.”’ 
” BLackMAn, F. F., and Smita, A. M., amare oe on vegetable 
accimi hanocec 
d respiration: VIII. Sue method for 
of submerged plants; LX. On assimilation in ahinens water planta and its velattoni 
to the Sica aseleel of carbon dioxide and other factors. Proc. Roy. Soc. London 
B 83:374-412. IQIt. 
