PHYSIOLOGICAL CHARACTERISTICS OF AXIATE PATTERNS 89 



original temperature the most highly positive region shows a greater "re- 

 bound" than lower levels (differential recovery). 



The root tip shows an essentially similar relation between potential 

 difference and local deprivation of oxygen. Removal of oxygen from about 

 regions of the root which have oppositely oriented electric polarities pro- 

 duces opposite effects on the potential of the whole. Removal of oxygen 

 from the region of active cell division at the root tip greatly decreases and 

 often reverses the potential difference between this and a lower root-level, 

 that is, the effect is differential (Rosene, 1934; Rosene and Lund, 1935). 

 Presence of a glutathione or SH-gradient in the growing tips of certain 

 plants has been reported (Camp, 1929); this perhaps indicates a gradient 

 in oxidative metabolism. Lund holds that the axial electric-potential 

 gradient results from a gradient in rate of oxidation. 



Determination of oxygen uptake and of flocculability of colloids in 

 parts of flowers show parallel respiratory and flocculation gradients cor- 

 responding to the morphological symmetry of the flower concerned. Re- 

 sults with bilateral flowers are particularly interesting: the gradients are 

 in the direction of the plane of symmetry. In leguminous flowers tested, 

 rate of respiration decreases and flocculability of colloids increases from 

 the superior to the inferior parts of the corolla; in some other bilateral 

 flowers the gradient is in the reverse direction (Zanoni, 1934a, b). 



Analysis shows gradients of various substances along the axes of the 

 higher plants. These, or some of them, are merely indicative of progres- 

 sive changes in physiological condition and progressive differentiation 

 with increasing distance from the growing tip. They are consequences of 

 the type of pattern characteristic of most plant axes, a growing tip re- 

 maining embryonic and continuously giving rise to new cells, all or a part 

 of which gradually differentiate. In general, it seems evident that physio- 

 logical gradients are characteristic and essential features of axiate pattern 

 of plants. Their presence can even be shown in single elongated cells of 

 some multiceUular axes, and they are present in multiaxiate unicellular 

 plants, such as Bryopsis. The axes of the higher plants are obviously 

 gradients, at least in the younger regions near the growing tips. When iso- 

 lated parts of a plant axis undergo reconstitution, these gradients play a 

 part in determining localization of shoots and roots. Doubtless, gradients 

 in roots and shoots and in other plant organs differ in character, but per- 

 haps the presence of a gradient is just as significant in relation to the prob- 

 lem of pattern as the character of the reactions which occur in it and the 

 chemical constitution of the substances involved. 



