294 Sc /lively — Contributions to the Life History of 



These facts to a certain extent are considered by Dar- 

 win. 12 He distinctly refers to the increased amplitude of 

 the circumnutation, noticeable by comparing the young 

 plant with the older stage, although the height of the 

 specimen is not always recorded in his tabulated results. 



May not the varying periods of movement be due to the 

 environment ? Is it not due to certain external conditions 

 that the manifestations of activity are now quickened, now 

 retarded ? 



Various writers, among whom is Dr. Macfarlane, 2 " have 

 shown in reference to experiments made upon Oxalis, 

 Cassia, Mimosa, etc., how important is the temperature 

 alone. Quick response to stimuli cannot be obtained, unless 

 care is taken to see that the thermometer registers from 

 75° to 105 ° F., according to the species. While this kind 

 of irritability is not here considered, we may rightly extend 

 the truth taught in this special case, to all phenomena 

 which may be classed under the manifestations of irrito- 

 contractility. To none are the above words more appro- 

 priate than the species now under consideration. 



If we watch the tip of the long stem passing through 

 space, as if reaching for a support, we may actually see it 

 move. Hour after hour it proceeds steadily onward like 

 " the hand of a clock." If we are fortunate enough to 

 see it touch a stick, we notice in a few hours a change 

 in the manifestation of its activity. It continues its course 

 now in a "beaten path," as it were, the influence of the 

 action still felt below, and being seen in the tightening 

 coils which clasp the stick. 



If the support be removed, the upper part at least of the 

 plant, slowly straightens and repeats the same searching 

 movements. My reader may say, " This i<s inherent in the 

 plant." True; these statements have only been repeated 

 in order to make very plain the exceedingly active proto- 

 plasmic conditions that exist in a climbing or twining plant. 

 Then, how much more easily does the physiological 

 equilibrium change with the variations in environment. 



