June 27, 1919] 



SCIENCE 



605 



in all of these stages, and consequently express 

 the action of imbibition and osmosis. 



The distinct action of imbibition and the 

 later joint action of hydration by osmosis and 

 by imbibition may be most readily recognized, 

 in organs in which the region of growth is 

 generalized as in the ovate flattened joints of 

 Opuntia or in such globular fruits as the to- 

 mato. The measurement of the growth of one 

 of these joints may be begun when it has a 

 lateral area no larger than the thumbnail, and 

 during this stage the increase is rapid and 

 shows a minimum disturbance from changes in 

 external conditions, as shown by the illustra- 

 tions. Growth continues throughout the en- 

 tire mass until an advanced stage of develop- 

 ment is reached, when it first slackens in the 

 basal portion. By this time large vacuoles have 

 been formed in the thin -walled cells, and water 

 loss from the surfaces of the organ has reached 

 such a rate that great daily variation in the 

 volimie results and actual shrinkage may en- 

 sue. A similar history may be predicated for 

 such structures as the large berry-like fruit of 

 the tomato, it being noted that the material in 

 both illustrations takes on solid matter and 

 water at such rate that not much alteration in 

 their proportions occurs during development. 



The enlargement of the trunk of a tree re- 

 sults from the multiplication and growth of 

 cambium and other cells on the outside of the 

 trunk directly inside and covered by the bark. 

 The trunk of the tree is in effect a cylinder of 

 moist but dead woody tissue surrounded by 

 a living sheath which becomes very active at 

 some time in the year and which as a result 

 forms an additional layer or sheet of wood on 

 the trunk which in cross section gives the ap- 

 pearance which has caused it to be designated 

 as an annual ring of growth. 



The actual course of growth or formation of 

 these annual cylinders or, more strictly speak- 

 ing, cones, has not imtil recently been mcas- 

 iired. In 1918 I was successful in making a 

 working model of a dendrograph which might 

 be attached to the trunk of a tree in such 

 manner that its changes in volume due to 

 whatever causes were traced on a ruled sheet 

 of paper carried by a revolving drum. The 



essential part of this apparatus is a yoke of 

 metal, which has two bearing screws resting 

 on the trunk and carrying a third contact 

 point on the end of the pen lever. It was not 

 possible to make a practicable instrument 

 until a yoke could be constructed which 

 showed but little variation as a result of 

 changes in temperature. Three alloys with a 

 very low temperature coefficient, bario C, 

 manganin and invar have been used and den- 

 drographs are now in operation on the trunks 

 of two species of pine, and oak, an ash, a syca- 

 more and a beech tree, and as these instru- 

 ments were placed in position before growth 

 began in 1919, there is every prospect that sea- 

 sonal records will be obtained from which the 

 principal features of growth may be seen. 

 Weekly records show that these trees do not 

 behave alike and that many conditions are 

 to be considered in interpreting the records. 



It is evident for example that but little is 

 known concerning the properties of bark as a 

 water-proofing or protecting coat for the tree. 

 The loose bark of the ash and pine trees seems 

 to allow such a great water loss from the sur- 

 face during the mid-day period as to cause 

 actual shrinkage which does not occur in trees 

 such as the beech and live-oak, which have a 

 perfect living green outer bark or skin. The 

 facts disclosed by these records can not fail 

 to be of interest in a discussion of any phase 

 of the complicated problem of the ascent of 

 sap. 



D. T. MacDougal 

 Desert Botanical Laboratory 



JOSEPH BARRELL 



American geology has lost one of its fore- 

 most leaders, one who promised to stand as 

 high as the highest. Professor Barrell's other 

 colleagues will tmdoubtcdiy agree with Pro- 

 fessor T. C. Chamberlin when he says : " We 

 had come to look upon him as one of the most 

 promising leaders in the deeper problems of 

 earth science. We feel that his early de- 

 parture is a very sad loss to our profession not 

 only, but to the whole group of sciences that 

 center in the earth and its constitution." 



