Book I. EVIDENCE OF VEGETABLE VITALITY. 257 



the winter season only, such as many of the mosses ; as well as by the dissection of the 

 yet unfolded buds at different periods of the winter, even in the case of such plants as 

 protrude their leaves and blossoms in the spring and summer, in which, it has been 

 already shown, there is a regular, gradual, and incipient developement of parts, from 

 the time of the bud's first appearance till its ultimate opening in the spring. The sap, 

 it is true, flows much less freely, but is not wholly stopped. Du Hamel planted some 

 young trees in the autumn, cutting off all the smaller fibres of the root, with a view to 

 watch the progress of the formation of new ones. At the end of every fortnight he had 

 the plants taken up and examined with all possible care to prevent injuring them, and 

 found that, when it did not actually freeze, new roots were uniformly developed. 



1665. Energies of life in plants like the process of respiration in animals. Hence it fol- 

 lows, that even during the period of winter, when vegetation seems totally at a stand, 

 the tree being stripped of its foliage, and the herb apparently withering in the frozen 

 blast, still the energies of vital life are exerted ; and still the vital principle is at work, 

 carrying on in the interior of the plant, concealed from human view, and sheltered from 

 the piercing frosts, operations necessary to the preservation of vegetable life, or protru- 

 sion of future parts ; though it requires the returning warmth of spring to give that 

 degree of velocity to the juices which shall render their ihotion cognizable to man, as 

 well as that expression to the whole plant which is the most evident token of life : in the 

 same manner as the processes of respiration, digestion, and the circulation of the blood 

 are carried on in the animal subject even while asleep ; though the most obvious 

 indications of animal life are the motions of the animal when awake. Heat then 

 acts as a powerful stimulus to the operations of the vital principle, accelerating the mo- 

 tion of the sap, and consequent developement of parts ; as is evident from the sap's 

 beginning to flow much more copiously as the warmth of spring advances, as well as 

 from the possibility of anticipating the natural period of their developement by forcing 

 them in a hot-house. But it is known that excessive heat impedes the progress of 

 vegetation as well as excessive cold ; both extremes being equally prejudicial. Hence the 

 sap flows more copiously in the spring and autumn than in either the summer or winter; 

 as may readily be seen by watching the progress of the growth of the annual shoot, which, 

 after having been rapidly protruded in the spring, remains for a while stationary during 

 the great heat of the summer, but is again elongated during the more moderate temper- 

 ature of autumn. 



1666. Artificial stimulants. There are also several substances which have been found 

 to operate as stimulants to the agency of the vital principle, when artificially dissolved in 

 water, and applied to the root or branch. Oxygenated muriatic acid has been already 

 mentioned : and the vegetation of the bulbs of the hyacinth and narcissus is accelerated 

 by means of the application of a solution of nitre. Dr. Barton of Philadelphia found 

 that a decaying branch of Liriod^ndron tulipifera, and a faded flower of the yellow iris, 

 recovered and continued long fresh when put into water impregnated with camphor j 

 though flowers and branches, in all respects similar, did not recover when put into com- 

 mon water. 



1667. Irritability. Plants are not only susceptible of the action of the natural stimuli 

 of light and heat, exciting them gradually to the exercise of the functions of their dif- 

 ferent organs in the regular progress of vegetation ; they are susceptible also of the action 

 of a variety of accidental or artificial stimuli, from the application of which they are 

 found to give indications of being endowed also with a property similar to what we 

 call irritability in the animal system. This property is well exemplified in the genus 

 Mimosa ; particularly in that species known by the name of the Sensitive Plant ; in the 

 Dionae^a muscipula, and in the Drosera. But sometimes the irritability resides in the 

 flower, and has its seat either in the stamens or style. The former case is exemplified 

 in the flower of the berberry and Cactus Tuna, and the latter in Stylidium glandulosum. 



1668. Sensation. From the facts adduced in the preceding sections, it is evident that 

 plants are endowed with a capacity of being acted upon by the application of stimuli, 

 whether natural or artificial, indicating the existence of a vital principle, and forming 

 one of the most prominent features of its character. But besides this obvious and ac- 

 knowledged property, it has been thought by some phytologists that plants are endowed 

 also with a species of sensation. Sir J. E. Smith seems rather to hope that the doctrine 

 may be true, than to think it so. ' 



1669. Instinct. Thez'e are also various phenomena exhibited throughout the extent 

 of the vegetable kingdom, some of which are common to plants in general, and some 

 peculiar to certain species, which have been thought by several botanical writers to exhibit 

 indications, not merely of sensation, but of instinct. The tendency of plants to incline 

 their stem and to turn the upper surface of their leaves to the light, the direction which 

 the extreme fibres of the root will often take to reach the best nourishment, the folding 

 up of the flower on the approach of rain, the rising and falling of the water lily, and 

 the peculiar and invariable direction assimaed by the twining stem in ascending its prop, 



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