Comparative Physiology. 193 



classes of plants. Yet, throughout the whole kingdom gene- 

 rally, the capability of division artificially and spontaneously is 

 characteristic of vegetables. There is perhaps no absolute dis- 

 tinction between the two kingdoms ; but it is the most obvious 

 and most general. The editor of Cuvier's Regne Animal thinks 

 vegetables and animals will be best separated by their products ; 

 the whole animal kingdom pi'oducing hard bony substances, 

 either internally, as in the higher classes, or externally, as in the 

 lower polypi. The duration of existence is in the higher 

 classes of plants very distinctive as comj)ared with animals. In 

 animals there is a period of matui'ity and decay, which we 

 cannot well arrest by any circumstances we can place them in ; 

 in plants, on the contrary, especially in Exogens, the period of 

 decay, in natviral circumstances, is greatly prolonged beyond that 

 of animals. By cutting in the tops and roots and removing the 

 soil, or by propagating from pieces of the plant, we can arrest 

 their decay to an apparently unlimited extent. It is no doubt 

 true that plants from seeds are generally more vigorous than 

 those from other portions of the plant ; but the long period in 

 which such plants as limes, poplars, &c., have been propagated 

 from pieces Avithout appearing much exhausted, seems to infer 

 a power of prolonging their existence to which there is nothing 

 comparable in animals. Even in annuals and biennials the life 

 of the individual may be much prolonged by preventing it 

 from fruiting, and by propagation of parts, in a much more ex- 

 tensive way than in the artificial or spontaneous division of the 

 lower animals, and to which there is no parallel case in the 

 higher. In plants it is the rule, in animals the exception. 



In enquiring into the way in which vital forces harmonise 

 or interfere with those common to other forms of inorganic 

 matter, he says : " In the structure of organised beings may be 

 detected an arrangement of the ultimate particles very different 

 from that which crystallisation produces in minerals ; it is a 

 mixture of solid and fluid substances, flexible and elastic, not 

 rigid and brittle like animals. In plants the solid substances 

 are more diffused through the body, more external than in ani- 

 mals, unless in the lower classes. The softest parts, and those 

 most subject to decay, are the j)laces where the activity of the 

 living principle is strongest, as in the spongioles of the roots of 

 plants, and the nervous matter of animals. No elementary sub- 

 stance, however, is found in these, which does not occur in the 

 inorganised world. The parent communicates to its offspring, 

 not so much the structure itself, as the power of forming this 

 structure from the surrounding elements. Of the fifty-four 

 elementary substances found in minerals, only eighteen or 

 nineteen are found in plants and animals ; many of these in 

 extremely minute proportions, though, perhaps, not the less ne- 



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