T. C. Broyer 191 



visualize a mosaic structure of the protoplasmic surface in space, while 

 Briggs has proposed a structural difference with time (here especially for 

 cation vs. anion absorption). Phase inversion or time change in struc- 

 ture would suggest that permeability changes might be sudden and the 

 delicate balance would in all probability be very easily disturbed so that 

 the whole of the protoplasm would go to one or the other of the con- 

 ditions. Such a weakness is not inherent in the mosaic structures in 

 space, although the latter may be difficult to envision. The viscosity and 

 electrical charge of the limiting surfaces have been considered by some 

 to be of importance in permeability relations (74, 42). Brooks and 

 Brooks (9, page 138) quote researches indicating that the rate of pene- 

 tration of nonelectrolytes into cells is more rapid than that of electro- 

 lytes; however, little direct comparison has been made. That perme- 

 ability to electrolytes relative to the rate of growth is significant and 

 appreciable is evident from the inorganic composition of plant tissues. 

 Any general theory must account for the entry of ions or ion pairs as 

 well as that of acid and basic dyes or compounds of low dissociation in 

 water. Certainly no single permeability hypothesis thus far proposed 

 will account for the penetration of solutes into living cells. Probably 

 several, if not all, of the suggested theories are simultaneously involved 

 in varying degree, depending upon the circumstances within the spe- 

 cific protoplasm concerned and the substance under absorption study. 

 Some detailed reviews have been made by Brooks and Brooks (9), 

 Stiles (80), and others (jy, 33, 5J, 54, 86). 



ROOT ANATOMY 



Relatively little research has been made on the relationship between 

 root anatomy and the physiology of absorption. Some early anatomical 

 work was done by Rufz de Lavison (69). His observations caused him 

 to consider the endodermis of importance as a limiting surface for the 

 penetration of solutes to the vascular tissues. Several studies were made 

 by Priestley and his associates on the physiological anatomy of roots. 

 Priestley and Tupper-Carey (65) suggested the relative impermeability 

 of the growing point of the root to water and substances in aqueous 

 solution. In other publications (64, 72), this point was further stressed 

 as well as placing restriction to movement across the root on the dif- 



