232 



C. M. CHILD. 



2. Where the conditions of confinement are extreme, oblitera- 

 tion or reversal of the gradient is followed in one or two days 

 by death with a basipetal gradient, but under less extreme con- 

 ditions the alteration of the gradient is followed by the separa- 

 tion of the axis into individual cells or occasionally small cell 

 groups, the separation beginning apically and progressing 

 basipetally. 



3. Obliteration or reversal of the original axial gradient, 

 followed by cell separation occurs, though more slowly, when 

 the plants are kept in open standing water and to a greater or 

 less degree, but still more slowly, in slowly running water in 

 diffuse daylight. 



4. A variable percentage of the isolated cells dies, the death 

 rate being in general highest in apical cells and decreasing with 

 the level of the cell in the axis, at least to the middle levels, 

 below which there is often little difference. The cells which do 

 not die may undergo a new development, giving rise to new 

 apical cells and so to new axes. 



5. Determinations of the susceptibility gradients in these 

 reproductive developments from isolated cells show that the 

 new apical cell arises from the region of highest susceptibility in 

 the old cell. This region is more commonly basal than apical, 

 because the gradient is usually reversed at the time of cell 

 separation, but both ends of the cell may give rise to new apical 

 cells where double opposed gradients exist. Rhizoids, on the 

 other hand, arise from low levels in the axial gradient. 



6. These experiments show that the original polarity of the 

 cells of Griffithsia can be completely obliterated or reversed, and 

 that the morphological development of new axes is an expression 

 of gradient relations present in the cell at the time. 



7. The facts support the conclusion that a gradient in meta- 

 bolic rate, protoplasmic condition, or whatever we prefer to 

 call it, of which the susceptibility gradient is within certain 

 limits an indicator, constitutes physiological polarity in proto- 

 plasm, and that such a gradient is not an inherent property of 

 protoplasm, but may be determined and altered by external 

 factors. 



HULL ZOOLOGICAL LABORATORY, UNIVERSITY OF CHICAGO, 

 January, 1917. 



