in their Structure and Functions. 27 



only to contractility. They cannot be the result of elasticity, 

 or of any mechanical arrangement, for they entirely resemble 

 the phenomena which accompany muscular contraction, as 

 it is exhibited in the animal body. In conclusion, I may 

 remark, that the strongest indications of contractility are, 

 perhaps, perceived in the petals, stamens, and other organs 

 of the flower. Accordingly, we find that these are the most 

 animalised parts of plants ; for their chemical composition 

 agrees with that of muscular fibre, the ultimate elements of 

 which consist of carbon, hydrogen, oxygen, with a large pro- 

 portion of azote. 



That many of the movements of plants are purely mechani- 

 cal there can be little doubt; we may take, for example, the 

 movements of the Celosia, and those of the Parietaria, and 

 of many others : but that those I have enumerated are the 

 result of contractility, and of contractility alone, cannot, I 

 think, for a moment be questioned. But perhaps it will be 

 argued, that, if we assign to plants the property of contractility, 

 we must likewise endue thern with a nervous system ; because, 

 according to some physiologists, muscular contraction cannot 

 take place without the intervention of nerves. They affirm, 

 that, when a muscle is operated upon by a stimulant so as 

 to be excited to contract, the impression is not, in the first 

 instance, made upon the muscular fibre itself, but that it is 

 first received by the nerves connected with the muscle, and 

 then transmitted by them to the muscular fibre. It will be 

 seen, however, from various facts which I shall state, that this 

 opinion is not correct, and that the property of contractility is 

 totally independent of the agency of the nerves. In the first 

 place, it is well known that the heart is formed a considerable 

 time before the brain ; for, if the chick in an egg be attentively 

 examined during the earliest periods of existence, the only 

 mark of life that can be perceived is a small beating point, called 

 the punctum saliens. This point gradually expands, and is 

 converted into the muscular substance of the heart. It is not, 

 however, until some time after the heart has been seen to 

 pulsate that the brain and nervous system become visible : so 

 that it is evident that the action of the heart is independent 

 of the influence of the nerves. In the second place, we know 

 that the quantity of nerves with which the heart is supplied 

 bears no proportion to its degree of contractility. Thirdly, 

 the heart, and many other muscular parts, long after they are 

 removed from the body, will contract very forcibly on the 

 application of a stimulant. Fourthly, mature foetuses have been 

 born, in whom there was no vestige either of a brain or a 

 spinal cord ; and it has been shown by experiment that the 

 heart will continue its contractions, as usual, for some time 



