1905] CURRENT LITERATURE 473 
The pioneer plant of the drifting sand is the delicate annual, Polygonum are- 
narium; a Veronica and a Tragopogon are other early plants. No grasses appear 
among the pioneers, though a Festuca appears the second year, with a Euphorbia; 
before long, these later species form mats and exclude the first named. When 
the dunes have become well covered with vegetation, and rather thoroughly 
established, they are termed Sandpussten. Plants found exclusively in sand 
are termed psammophytes, while those found elsewhere but preferring sand 
are termed psammophiles. The photographs accompanying the paper well 
illustrate the dunes and the Pussten.—H. C. CowLes 
A series of five papers by Brown and Escomse record the fundamental 
Tesearches made by these investigators at Kew during a period of three years, 
The paper here cited? is the largest of the series and to it the others are supple- 
mentary. Part I is descriptive of apparatus devised by the authors for accurately 
determining the amount of CO, in air before and after photosynthesis. The 
tate of photosynthesis as determined by the direct measurement of CO, entering 
was found to be one-third to one-fifth that found by Sacus with his method of 
increase in dry weight. When all sources of error were accounted for, the dis- 
crepancy was reduced to 50 percent. An investigation of SAcHs’s method shows 
that the errors are cumulative, so that it is very unreliable. T he estimation of 
foliar respiration as made by the authors agrees. with that made by BLACKMAN. 
An investigation of the “energetics” of the leaf shows that only a small part of 
the radiant energy incident upon a leaf is used for photosynthesis, the _ Sem 
coefficient” being only 6.5 per cent. in full sunshine. Even in moderate light the 
Supply of photosynthetic energy is far greater than the leaf can use. The surplus 
of energy which the leaf is compelled to absorb is dissipated by the vaporization 
of water in transpiration and by the thermal emissivity required in the constant 
adjustment of the temperature of the leaf to that of the surrounding air.—RAYMOND 
H. Ponp. 
AT THE suggestion of Professor WITTROCK, HessELMAN?® undertook the 
completion of an investigation begun by STENSTROM, but broken off upon the 
latter’s death in rgor. Having noticed that in Sweden southern slopes are often 
n and that birch woods ascend 
determined upon a 
careful study of the distribution of plants on slopes of various directions. He 
chose for this study railway embankments, because 
all kinds of slopes. The results obtained were very t 
having chiefly xerophiles or weeds (such as Anthemis 
arvensis, Barbarea vulgaris), and northern slopes having 4 more 
.. . . 
45 Brown, H. T., and Escomse, F., Researches on some of the physiological 
Processes of green leaves, with special reference to the interchange of energy between 
the leaf and its surroundings. Proc. Roy. Soc. B. '76:29-112- 1995. S 
26 Hessetman, H., K. O. E. Stenstrém’s Studier dfver Expositionen 
tande pa Vegetationen. Arkiv for Botanik 4:1-54- 1905. 
s tinctoria, Convolvulus 
closed and 
s Infly- 
