192 The Irish Naturalist. Nov. Dec, 



perfoliata is not, what it would prima facie appear to be, 

 an instance of that direct response to the stimulus of sun- 

 light so familiar to us in many species of flowering plants. 

 How then are we to explain this action which synchronises 

 with the diurnal advent of sunlight yet has no direct causal 

 connection with it ? It must, I think, be regarded as an 

 example of plant-habit, of memory-like or mnemic activity, 

 to use the language of Semon's theory ^ so ably discussed 

 by Francis Darwin in his presidential address to the Dublin 

 Meeting of the British Association in 1908. Having 

 declared the characteristic par excellence of habit to be 

 a " capacity acquired by repetition of reacting to a fraction 

 of the original environment," the President thus proceeds : — 

 " When a series of actions are compelled to follow each 

 other, by applying a series of stimuli, they become 

 organically tied together or associated, and follow each 

 other automatically, even when the whole series of 

 stimuli are not acting. Thus, in the formation of habit 

 post hoc becomes equivalent to propter hoc. Action B 

 follows action A, because it has been repeatedly compelled 

 to follow it." 



On this view the periodic opening and closing of the 

 Chlora perfoliata flowers may be regarded as a character or 

 habit originating in an ages-long succession of recurrent 

 light stimuli received at some remote stage in the history 

 of the species. The habit has long since become so in- 

 grained in the constitution of the plant as to operate auto- 

 matically at a certain stage of growth. It is, in fact, 

 one of that bundle of potentialities mysteriously wrapped 

 up in the seed, which ordain that the germ of Chlora perfoliata 

 shall produce precisely that and none other of the 100,000 

 or so of phanerogamic species which clothe the earth. 



As this explanation obviously implies the inheritance 

 of acquired characters it cannot be accepted by those w'ho 

 deny the possibility of such inheritance. They may perhaps 

 take refuge in the supposition that this capacity of the 

 Chlora flower is acquired by each individual plant within 

 the space of its brief life-time as an annual, that the capacity 



^ Richard Semon, Die Mneme als erhaltendes Prinzip im Wechsel 

 des organischen Geschehens. Leipzig, 1904. 



