1862.] on Motion in Plants and Animals, 437 



plants, — as the Oscillaiorice^ — but are met with amongst the most 

 highly organized members of the vegetable kingdom. The movements 

 of sensitive plants, various species of Mimosa, of Dionaea Muscipula, 

 of certain tropical species of Desmodium, of the stamens of Berberry, 

 &c., can be referred only to vital contractility of certain of their 

 tissues. Whatever obscurity may hang over these, let it be remarked 

 that there is the same evidence of the nature of this vital contractility 

 in plants as in animals. It is dependent on life, and not, like any 

 physical property, retained so long as the structure itself is not 

 destroyed. So, also, these movements either occur spontaneously, or 

 may be excited by various stimuli — touch for example. If these 

 motions depend upon elasticity or hygroscopic changes, or any other 

 physical cause which elsewhere operates, how could stimuli act to 

 produce them ? Moreover, they appear to be governed by the same 

 laws that regulate their action in the animal kingdom. Their energy 

 varies with the vigour of the plant. Excessive exercise produces 

 exhaustion, but the power is restored during subsequent repose. This 

 evidence, thus clear and satisfactory, receives a remarkable and most 

 interesting confirmation from the effects produced by the vapour of 

 chloroform. 



Now, it would be startling to talk of the muscles of plants, but, 

 nevertheless, we see that a structure endowed with vital contractility 

 occurs in them. This is simply a question of the relation of the term 

 muscle to contractile tissue. The term must either be limited to 

 certain forms only of contractile tissue in animals — and it may be 

 doubted whether it be practicable even thus arbitrarily to define its 

 application — or it must be extended to the contractile tissues of plants. 

 At all events it is obvious that we can draw no physiological distinction 

 between the contractile tissues of plants and animals. 



The contractile tissues of the higher animals are indeed capable of 

 being excited to activity by a peculiar stimulus — the nerve-force ; but 

 this special stimulus does not exclude the operation of others, and, 

 what is nearer to our purpose, there is no more evidence of the opera- 

 tion of nerve-force exciting vital contractility in the substance of the 

 simplest animals than in plants. 



After excluding from both kingdoms all those movements which 

 are due either to extraneous causes, or simply to the physical properties 

 of a tissue, there still remains in the vegetable, as in the animal 

 kingdom, motion which unquestionably depends on vital contractility, 

 and this is perhaps the most universal attribute of living beings. 



[W. S. S.] 



