PALEONTOLOGY-PHYSICS. 405 



in the structural and plastic sense; and so far has this general result 

 been pushed that to-day the value of gj^mnosperm leaf species in our 

 conceptions of past change is perhaps fourfold what it was when these 

 investigations were begun. A point has been reached where the 

 discovery of the structure of a single antecedent dicotyl stem of the 

 early Jurassic would be of momentous importance. 



Primarily the fossil plants afford a much-broken record of descent 

 and of past distribution. They are a chief index of former climates; 

 and, very distinctly through the work of Clements, the data of palaecol- 

 ogy come into view. In the newer and broader field the facts of both 

 the animal and the plant record must constitute a well-founded 

 palseobiology. Perhaps the manner in which this fossil evidence solves 

 or promises to solve abstruse problems which botanists alone are 

 hardly in a position to attack may be simply illustrated by asking the 

 question whether the great size of magnolia flowers, or of the cones 

 of certain conifers and cycads, is primitive or not. Evolutionists 

 would like to know. This question is really of crucial importance. 

 Now, the fossil e\'idence so far found at least shows that it "udll not do 

 to rest content with interpreting the flowers of a form like the Mag- 

 nolia campbelU or the huge cones of Pinus coulteri as mere examples 

 of gigantism. The cycadeoid flowers show that great cycles of re- 

 duction in organs of fructification are a possibility to be reckoned with, 

 and further discoveries indicating the trends of past floral changes in 

 the simple feature of bulk and seed output are eagerly awaited. 



This year has been given to general field work in Mesozoic and 

 Tertiary ''bad lands" areas east of the Rockies as a member of Dr. 

 Clements's party, to some special field work in Wyoming, to some 

 general observation of the living and fossil conifers of Cahfornia and 

 Arizona, and to work on manuscripts, without any major subject being 

 brought near to publication. 



PHYSICS. 



Barus, Carl, Brown University, Pro\ddence, Rhode Island. Continuation of 

 investigations in inter jerometry. (For previous reports see Year Books 

 Nos. 4, 5, 7-18.) 



During the year, Professor Barus has been occupied with apphcation 

 of interferometry to a variety of gravitational experiments. The 

 main featiu-es of the first group of these have already been com- 

 municated (Science, vol. 50, pp. 214, 279; Proc. Nat. Acad. Sci., vol. 5, 

 p. 547, 1919). They relate to the motion of a gravitation needle in a 

 viscous medium like air, to the possible determination of the New- 

 tonian constant in terms of the viscosity of air, to the remarkable 

 pervasiveness of radiant forces arising in temperature changes of the 

 environment, to the beha\ior of the needle in a vacuum, etc. 



