I io PLANT RESPONSE 



being continued. It is important to note that the two records 

 were taken with the same specimen, and in immediate suc- 

 cession to each other. The first, or upper, records the 

 response of the leaf to a single stimulus and its recovery ; 

 the lower gives the response to continuous stimulation. In 

 appearance the two records are singularly alike. But though 

 the leaf at the end of each response occupies the same 

 position, the molecular conditions in the two cases are, as 

 will be shown presently, entirely different, inasmuch as in 

 the first, renewed response was immediately obtained, thus 

 showing its sensitive condition ; while in the second, the 

 organ was insensitive, and could give no response until after 

 a period of rest of about ten minutes. 



The explanation of this apparent anomaly is quite clear 

 from the experiments which have already been described, 

 showing that under continuous stimulation the normal longi- 

 tudinal contraction undergoes reversal and passes into relaxa- 

 tion, as is also the case with continuously excited muscle, 

 the motile response of Mimosa being only an instance of 

 differential longitudinal contraction. We obtain here also the 

 usual sequence of first, normal contraction, and second, the 

 fatigue-relaxation, or posture of erection. 



To sum up, then, it is clear that our association of the 

 erect position with sensitiveness is not always correct, for the 

 leaf may assume this posture as the result of fatigue. That 

 its position in this case, however, though outwardly imitating 

 that of sensitiveness, is profoundly different, is at once 

 revealed on application of stimulus. The leaf is now irre- 

 sponsive. But if we allow it a period of rest — of some eight 

 or nine minutes in summer, or double that time in winter — 

 the internal molecular equilibrium is re-established. But of 

 this internal readjustment the leaf gives no visible indication. 

 It remains in the same unchangingly erect position. During 

 the course of the cycle, then, it has passed from the normal 

 erect to the normal depressed, and thence to the abnormal 

 erect position. It next passes, without any outward change, 

 from this abnormal erect to the normal erect position, after 



