209 



acteristic of most such bundles, and there is no indication of the 

 well-marked, clearcut pattern of sieve cells and companion cells 

 found in every Zea cauline bundle. 



In line with the expressed purpose outlined in the preface, 

 the text presents in more positive form than some other texts the 

 author's preferences among various more or less debatable concepts. 

 For example, in explaining the rise of liquids in stems, after pre- 

 liminary discussions during which certain vital factors and root 

 pressure are admitted as possible minor factors, the authors set 

 up "the cohesion of water theory" as an almost completely satis- 

 factory explanation and state that "At the present time most plant 

 physiologists are agreed that the cohesion of water theory is a 

 correct representation of the principle mechanism by which water 

 is transported through plants, be they the tallest of trees or herbs 

 only a few feet in height." To a reviewer who is not a plant physi- 

 ologist, it is difificult to see how the tensile strength of any elongate 

 column, water or wire, can be counted as anything but secondary 

 to the force or forces which exert the necessary pull at the top of 

 the column. Imbibition seems not even to be accorded mention 

 among possible factors. 



While the selection of specific theories for substantial support 

 and preference is justifiable and desirable, it is likely to raise ques- 

 tion of dispute on the part of other botanists, who may have their 

 own pet theories or who may feel that for some given phenomenon, 

 no positive stand is justified. For the reviewer, such a case is illus- 

 trated by the following statement : "No reputable botanist has held 

 for generations, for example, that plants obtain their food from the 

 soil, yet this and other fallacious beliefs are still widely entertained 

 among the general population." The question at issue is, of course, 

 primarily one of semantics and pedagogy, but the reviewer, what- 

 ever his category, admits to a pet aversion against this particular 

 limitation of the meaning of the word, food. Moreover, he would 

 even hold that botanically and chemically the definition of the 

 word, food, must be expanded to include water and minerals, not 

 to mention thiamin, root-absorbed glucose, etc. 



Another point in which semantics is perhaps more involved 

 than fact is found in the discussion of guttation. "The drops of 

 guttation water which form at the tips of grass blades and the tips 

 and edges of the leaves of other plants are often erroneouslv con- 



