58 CARNEGIE INSTITUTION OF WASHINGTON. 



of dispersion may vary widely, but still absorb water. This picture 

 of the cell expanding by the osmotic action of electrolytes in the 

 Uquids and by the swelling resulting from imbibition or hydration 

 of its colloids would not be complete without some delineation of the 

 effect of the increasing changes within its mass. 



Nowhere is metabolism more active than in the embryonic grow- 

 ing cell. The dissociations which are usually included in the con- 

 ception of respiration may be taken to concern molecules of material, 

 already present in the more liquid phase of the colloid or newly intro- 

 duced. The splitting of the sugars results in the formation of acids 

 as one stage of the process, and if the succeeding stages are impeded 

 such material accumulates and acidosis results, with new temperature 

 relations which may profoundly affect imbibition and the enlargement 

 constituting growth. These changes exemplify but do not exhaust 

 the possibilities of modifications of the colloidal action in growth. 



The Nature and Course of Growth in Higher Plants, hy D. T. MacDougal. 



The development and standardization of the auxograph, which 

 has been one of the principal instruments of research in these labora- 

 tories during the last few years, have made it possible to make meas- 

 urements of changes in volume of organs of diverse origin and pre- 

 senting different anatomical conditions. It has become evident, as 

 a result of the comprehensive series of observations thus made avail- 

 able, that much of the present confusion as to the main features of 

 growth arises from the fact that attempts have been made to com- 

 pare and harmonize growth in organisms presenting physical condi- 

 tions not really comparable. 



Thus the growth of bacteria consists in the enlargement to a unit 

 size of cells which become independent upon maturity, while growth 

 in the higher complex plants entails the multiplication of embryonic 

 cells and the development of the greater number of them into special 

 static tissues to which the growing cells remain attached. An instru- 

 ment applied to the terminal or growing portion of a higher plant thus 

 records the changes in volume not only of the newest and youngest 

 embryonic cells, but also of other tracts in all series approaching 

 maturity. The implied distinctions and corrections must be made in 

 any general discussion of the physical features of growth. 



During the past year measurements under controlled and cali- 

 brated conditions have been made of the growth of such organs as 

 the succulent leaves of Mesemhryanthemum, the rapidly growing 

 stems of the sunflower (Helianthus), pods of the bean {Phaseolus), 

 and fruits of the potato (Solarium). The data obtained in this man- 

 ner furnish a basis for the generalization that organs or members, 

 when in a young condition and consisting entirely of embryonic 



