214 C. M. CHILD. 



to determine their effect upon the developmental and morpho- 

 logical order in the plant body. In the present paper some 

 experimental alterations of the gradient which do not necessarily 

 end in death are described, and some evidence concerning the 

 effect of these changes on further development and axiation is 

 presented. This is merely the first step toward the experi- 

 mental determination of the relation between the axial gradient 

 and polarity in the plant and the very simple experiments de- 

 scribed here serve chiefly to point the way to more exact deter- 

 mination and control. 



For experimental purposes a form with large cells and sensitive 

 enough to react readily to environmental changes but not too 

 sensitive was desirable. I am indebted to Professor Osterhout 

 for calling my attention to Griffithsia, w r hich has proved to be of 

 interest in various w r ays. 



THE GRIFFITHSIA Axis AND GRADIENT. 



The cell outline of an average, well-developed vegetative axis 

 and branches from the material employed is indicated in Fig. I, 

 the hairs (Child, '17) being omitted. The method of growth 

 is evident from the figure. The apical cell grows to a certain 

 variable size and divides into a very small apical cell which 

 repeats the process of growth and division, and a larger sub- 

 apical cell, which continues to grow, but does not divide unless 

 it later gives rise to a new axis by the separation of a new apical 

 cell from some point of its apical region, as in the formation of 

 new branches (Fig. i). At a greater or less distance from the 

 apical end a secondary basal elongation of the cells begins and 

 is evident in the progressive change of shape of the cells toward 

 the basal end of the axis (Fig. i). 



As already noted (Child 'i6e), the general susceptibility gradi- 

 ent in such an axis and in each branch is basipetal when the 

 plant is in good condition. In the apical third or half of the 

 length the gradient is very uniform, but in the basal region 

 irregularities occur consisting in a susceptibility in one or more 

 cells above or below the expectation corresponding to the level 

 of the cell or cells. In the two or three most apical cells the 

 intracellular gradient is usually slight or sometimes not visible, 



