9 6 THE NA TU RE-STUD Y RE VIE IV [ 2 : 3 — march, 1906 



in subject-matter, as well as in method as already indicated. I believe that the 

 coming successful nature-study will have a decidedly industrial tendency in that 

 it will deal largely with the every-day nature as it closely affects human life ; and 

 although we cannot now foresee just how the details will be worked out, it seems 

 reasonable to believe that there must be developed a very close connection between 

 what we may call industrial nature-study and industrial manual training. 



THE SAP CURRENT: AN EXPERIMENT 



BY F. L. STEVENS 

 Professor in N. C. College of Agriculture and Mechanic Arts 



Few of the phenomena of plants are so little understood, or so 

 much misunderstood, as that of the sap current. Since the time of 

 Liebig there has been misconception as to the nature of respiration 

 in plants, and respiration has been sadly confounded in the minds^ 

 of many teachers and most pupils, and even in some reputable text- 

 books, with carbon assimilation. This misconception is now giving 

 way. Knowledge of the sap current, however, is not so rapidly 

 becoming general. 



If you will put the question, " What effect will girdling a branch, 

 that is, removing all of the bark clown to the wood, have?" to a 

 class of pupils of any grade from the primary school to the univer- 

 sity, the answer almost invariably will be that "those portions of 

 the branch lying beyond the girdle will die." Your class will go 

 even further and give an explanation for the assumed dying, by stat- 

 ing that the sap current which passes through the bark is interrupted 

 and the water supply of the leaves cutoff. Such an answer would also 

 almost invariably be received if the question were put to a body of 

 practical farmers or horticulturists, men accustomed to handling 

 plants. Yet a more erroneous belief could hardly be imagined; for 

 as a matter of fact, the branch beyond the girdled portion does not 

 wilt under these conditions. The explanation offered for the sup- 

 posed wilting is, of course, totally fallacious. 



So sure is your class that wilting will occur, and so sure are they 

 of the correctness of their explanation that an experiment upon this 

 subject is particularly attractive. They are certain that they know 

 what the results will be, and consider the experiment childishly sim- 

 ple, utterly useless. As the days go by, however, they find their pre- 

 dictions unfulfilled. Then their confidence changes to uncertainty 

 and finally to wonder, and their minds enter upon a condition ex- 





