568 BOTANICAL GAZETTE [JUNE 
venter which lies below the surface of the prothallium and a straight neck 
which projects as a short tube beyond the surface. The organization of the 
axial row was not worked out in detail. One figure shows an archegonium 
with an egg and two free nuclei in the neck canal. 
In minor features the two genera differ. In Tmesipteris the archegonia are 
much more numerous than the antheridia, while in Psilotum the reverse is true. 
The archegonia and antheridia of Tmesipteris are about twice the size of those 
of Psilotum. The statement that the gametophyte generation of the Psilo- 
taceae bears no structural resemblance to the prothallium of Lycopodium or 
Equisetum seems peculiar. We readily agree that there is no suggestion of 
Equisetum characteristics, but both the descriptions and the numerous excel- 
lent figures constantly remind one of Lycopodium, especially of the L. Phleg- 
maria type. LAWSON closes with the remark that no new facts were revealed 
which would discount the view, now generally held, that the Psilotaceae are 
more nearly related to the extinct Sphenophyllales than to any other known 
group of pteridophytes. This may be true, for the prothallia of the Spheno- 
phyllales are entirely unknown.and probably will remain so; but if they should 
be discovered, we should expect them to be of the Equisetum type. As far 
as the evidence of prothallia goes, we should guess that it indicates relationship 
with the Lycopodiales. The investigation of the embryogeny will be awaited 
with interest, since it will have a more definite bearing upon the problem of 
relationships.—CHARLES J. CHAMBERLAIN. 
Photosynthesis.—Brown and Hetses have made a careful study of the 
experiments of various investigators on the relation of light intensity to photo- 
synthetic rate. They conclude that “the published work on photosynthesis 
does not warrant the general conclusion that carbon dioxide assimilation in 
plants is proportional to the light intensity. Instead they indicate a progres- 
sively smaller augmentation of the rate of assimilation for each increase in light 
intensity. This decrease in rate of augmentation continues until a point is 
reached at eee further increase in light produces no measurable increase in 
assimilatio 
Baby pee Hetse® have also scrutinized the literature on the effect of 
temperature on photosynthetic rate and have come to the following surprising 
conclusions. The temperature coefficients (Qi) lie between 1 and 1.4. 4 
are smaller than those for most vital phenomena which have values agreeing 
with the Van’t Hoff law. These coefficients are of a magnitude that indicates 
that seesieakdenesrncey is a purely photochemical process. 
5 Brown, W. H., and Hetse, G. W., The relation between light intensity and 
carbon dioxide sisteiation: Philippine Suni: Sci. 12:85-95. 1917. 
———, The application of photochemical temperature coefficients to the 
sides of catbon dioxide assimilation. Philippine Jour. Sci. 12:1-24. 1917. 
