io PLANT PHYSIOLOGY 



variation in thickness, whether they be primary or secondary roots ; they 

 permeate large masses of soil, but do not lay these completely under con- 

 tribution, because the absorptive apices are relatively few in number. In 

 another type (e.g. Beech) the roots are much more richly branched, and hence 

 a far greater number of absorptive ends are present in the same area. Further, 

 in this case the lateral roots are always thinner than the primary roots ; they 

 permeate smaller masses of soil, but make greater use of them. 



In some roots the ordinary epidermal cells act as water absorbers, but in 

 the majority of cases the absorbent cells are tubular outgrowths of the outer 

 layer of cells, the so-called root-hairs. These are often of considerable length, 

 and have the effect 



1. 49, after period read as indeed does the root epidermis also as a rule. 



1. 50, after with difficulty, read inasmuch as the contiguous hypodermal 

 cells, for the most part, become suberised, sooner or later. 



I. 56, for 1865 read Lectures, p. 257 



29, 11. 38-43, for ' If we assume . . . trickling away read ' Naturally water 

 particles are held the more firmly by the soil the nearer they are to the 

 surfaces of the particles of which the soil is composed. 



30, 1. 3, heading of middle column should read, Original amount of water in 

 g. retained by 100 g. of dry soil. 



II. 52-4, delete In reality ... of the cell-wall. 



31, 1. 5, delete thus 



32, 1. 21, after root read (compare, however, the observations of URSPRUNG, 

 1906, p. 518). 



11. 23-4, for we are thus compelled ... of water read we are thus com- 

 pelled to believe that the vital activity of protoplasm plays a very important 

 part in the absorption of water as well as in that of substances dissolved in 

 it (Lecture II). 



11. 47-54, delete This cuticle ... is entirely absent. 



33, 11. 2-4, for The cuticle . . . SCHWARZ, 1883) read The epidermis of the 

 root, on the other hand, has no cuticle, and its outer walls are thus easily 

 permeable to water (KROMER, 1903). 



I. 8, for (HALES, 1748, p. 78) read (HALES, 1731-3, chap. I). 



II. 19-21, delete In this instance ... by transpiration. 



I. 31, for ignored. In tropical regions read ignored (BURGERSTEIN, 1904) 

 This is true even of plants like Dipsacus, whose fused leaf margins form recep 

 tacles often filled with water (RosxocK, 1904). In desert plants, on the other 

 hand (VOLKENS, 1887 ; SPALDING, 1906), the absorption of dew by aerial parts 

 may be of some significance, and in tropical regions, 



II. 54-5, delete These hairs . . . Flora, 94, 464). 



34, 11. 14-16, for The whole plant . . . grey colour read The whole plant is, 

 however, covered with hairs such as occur on the leaf bases of other forms, 

 and it is by these that it absorbs all the water it requires. (As to the mechanics 

 of the water absorption, see MEZ, 1904 ; STEINBRINCK, 1906 ; and Lecture 

 XXXII.) 



Bibliography, for HALES. 1748, &c. read HALES. 1731-3. Vegetable 

 Staticks. London. 



P. 36, 1. 6, for e.g. BURGENSTEIN, 1887-1901 read (see BURGERSTEIN, 



1904), 



I. 13, for uniform, and read and at the same time 



II. 16-17, /or it ma y be ... loss of water read the decrease in weight from 

 hour to hour may be considered to be a direct measure of the loss of water. 



