CflAPTER I 



THE PLANT AS A MACHINE 



Responsive movements in plants -Work done by plant — Plant as a machine 

 — Indicator-diagrams - Physiological response-curves — Pulse-records — Cardia- 

 grams— Modification of pulse by poison and other agencies— Automatic 

 response in plants— Optical Lever Recorder — Effect of external agencies on 

 automatic pulse-beat in plants. 



From the moment when the germinating secdh"ng bursts 

 its seed-coat, a complex series of movements is initiated. 

 The radicle turns downwards, the plumule up. Underground, 

 the root gropes its way towards moist places, and contrives 

 to avoid hard stones and obstacles. Above ground, the stem 

 is seen to bend, as if in search of light. Tendrils twine about 

 a support. These, amongst many visible movements, are 

 striking enough, but within the unruffled exterior of the 

 plant-body there are others, energetic and incessant, which 

 escape our scrutiny. 



Now all these activities are but so many expressions of 

 the response of the plant to the various stimuli by which 

 the living organism is constantly being excited. The plant- 

 organ sometimes responds locally to the direct impact of 

 stimulus, and at other times the effect is conveyed away by 

 conducting elements analogous to nerves, and the responsive 

 changes are manifested at a distance. Thus the most varied 

 and important functions of plant-life are brought about by 

 the power of the tissue to respond to stimulus, that is to say, 

 by the irritability of the plant-cells. 



In such fashion, work is performed continuously b)- the 

 organism, as if by a machine, and the magnitude of the work 

 performed is often very considerable, as is seen, for instance, 

 when sprouting seedlings break through a pavement. 



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