310 THE PI.ANT WORI.D 



Our Teachers' Department. 



Edited by Professor Francis E. Lloyd. 



Teachers College, Columbia University, New York City. 



POPULAR BOTANY. 



In Country Life in America for November, 1904, Mr. John F. Johnson 

 describes certain well-known movements experienced by Rhododendron 

 leaves when subjected to various degrees of low temperature. Thus, at 

 45 degrees, the leaves are in normal position ; at 17 degrees, the leaf- 

 stalks are bent downwards considerably and the leaf -blades are somewhat 

 curled longitudinally; when the thermometer reaches zero, both bending 

 and curling are still more pronounced. When a twig with curled leaves 

 is brought into warmed air (45 degrees), the latter uncurls in eight min- 

 utes " with a springing motion." 



The author goes on to say that : ' ' Nature has a purpose for all these 

 metamorphoses. Less transpiration and consequently less loss of heat is 

 the result of this curling. This power in living plants of conforming 

 to external circumstances is termed ' irritability.' Somewhat analogous 

 to the above is the closing up and ' sleeping ' of clover leaves at night. 

 Tulip leaves also exhibit this power of closing and expanding under dif- 

 ferent temperatures. When placed in a heated room, during sunshine or 

 mild weather, outdoors, the petals expand, but will contract and close 

 together when subjected to reduced temperature." 



I venture to call in question some of these statements, because they bear 

 evidence of the tendency often noticed of confusing popular botany and 

 botany which is not true to the facts. 



Perhaps we may not quarrel with a writer for personifying nature, 

 though in the opinion of many students this is not commendable. It is 

 certainly less so to attribute to nature thus personified the ability to form 

 a purpose. The underlying assumption in the first sentence under quo- 

 tation appears, further, to be that all ' ' metamorphoses ' ' of organisms are 

 purposeful, using the word in the meaning of useful. Now, this assump- 

 tion is in point of fact something to be proved or disproved. To be sure, 

 many students and writers — terms by no means synonymous — have 

 gradually come to believe that every organ and every character, of 

 whatever sort, has a definite use, or has had, or will have, and if any 

 inquiry is made it is naturally to find out this use, whereas the first 

 proper aim is to see if it has a use or not. The very spirit of science is 

 done violence to in this way. 



The critic may be uninformed as to this point, but he does not believe 



