60 CARNEGIE INSTITUTION OF WASHINGTON. 



have been adequate for the measurement of changes in volume of 

 stems, leaves, nuts, fleshy fruits, etc. It has been neccessaiy, however, 

 to perfect a separate design for attachment to the trunks of trees in 

 order to record daily and seasonal changes in diameter and form. 

 Two successful types of such an apparatus have now been in opera- 

 tion at the Coastal Laboratory for two months. Both types employ 

 a belt of wooden blocks 6 by 4 by 4 inches hinged together and fas- 

 tened securely as a supporting belt around the trunk of a tree. In 

 one type series of plungers in contact with a number of selected points 

 around the tree carry on their outer ends an encircling wire. Any 

 change in position of the plunger moves the encircling wire and the 

 motion is recorded by a pen on a suitable revolving drum. The sec- 

 ond type of dendrograph carries a yoke which encircles the trunk 

 of the tree with four points of contact. Changes in volume of the 

 trunk are followed by differences in distances between the contacts, 

 which are duly recorded as above. At present these instruments 

 have been used to obtain measurements from the oak {Quercus agri- 

 folia) and the Monterey pine {Pinus radiata). 



PHOTOSYNTHESIS AND METABOLISM. 

 Photosynthesis and Respiration, by H. A. Spoehr and Frances Long. 



It has become evident that further insight into the complex phe- 

 nomenon of photosynthesis is to be gained only by means of inten- 

 sive study of the process under very carefully controlled external 

 conditions and the elimination of secondary factors. For these pur- 

 poses simple, thin leaves have proved to be the best material. By 

 careful manipulation the mature leaf, isolated from the plant, can be 

 worked with for several days without conflicting or deleterious reac- 

 tions setting in. 



After extensive preliminary experimentation, a rather elaborate 

 apparatus has been devised and constructed for the accurate control 

 of the conditions of temperature, light, air-supply, and water-vapor. 

 The method now in use is based upon the differential determination 

 of the amount of carbon dioxide fixed by the plant. For this purpose 

 special apparatus has been devised for making exceedingly careful 

 determinations of carbon dioxide by means of absorption in barium 

 hydroxide. The solutions are titrated in an atmosphere free of carbon 

 dioxide. The leaf is contained in a special glass cell provided with 

 tubes for gas inlet and removal, as well as for the supply of nutrient 

 solutions. 



The features of the general problem which are now under investi- 

 gation are rather manifold, though all are closely coordinated and 

 interdependent. These comprise a study of the course of what might 

 be termed the basic metabolism of mature leaves and the influence 



