214 Comparative Physiology. 



in the Vegetable Chemistry, to which great additions are con- 

 stantly being made, should tend greatly to develope the subject 

 of the relation which bodies bear to each other, and facilitate 

 their classification into those leading groups which furnish a 

 comprehensive idea of the whole. 



Vital force does not always seem dependent on the usual 

 stimuli ; new bulbs and new tubers will be formed under ground 

 at times, without any foliage being developed to the light, the 

 little stimulus of heat and food being sufficient, without the 

 chemical powers of light, to perform the usual actions and form 

 a new being, though generally smaller, yet perfect.* It seems 

 also, in a certain degree, capable of being stored up, as plants 

 in cold climates push more strongly when growth commences ; 

 the longer light of the day, in northern regions, will hardly 

 account for the whole of the effect, and it is usually ascribed 

 to the increased excitability of the tissue. That the usual ope- 

 rations of growth carry with them a powerful stimulus in in- 

 creasing vital or organic force is clearly seen in the way stunted 

 and slow-growing plants are renovated in vigour. By cutting 

 back the yovmg shoots of last year's growth those of the succeed- 

 ing year are made to push more strongly ; a more vigorous 

 growth is made to commence, and is generally found to continue; 



* Connected with this subject also are the celebrated opinions of Mr. Main, 

 that the germ contains within itself all that will be developed from it in the 

 state of an invisible membrane. De Candolle, in his Vegetable Physiology, 

 quotes the opinions of Bonnet, which are similar, and does not state any ob- 

 jection, but rather seems to coincide. Miiller says the germ is not actually, 

 but only potentially, the same being. The germ itself is only formed of amorphous 

 matter; the earliest rudiments, he says, are distinct though simple; and the 

 later complicated state arises by transformation from the simple rudiment. 

 The word invisible, however, seems to set no limits, and it may be said the 

 simple visible rudiments contain the invisible future being. It has been said 

 the opinion is wrong, as the vital sap in the cambium exhibits living powers, 

 and it is this living power that organises, and not a developement of invisible 

 parts. Life, however, may be exerted in developing as well as organising ; at 

 least it is possible to conceive so, though not so consonant to the general ideas 

 of life. The aptitude of all vegetable matter to throw off a membrane, on 

 being extravasated or cut, would seem to countenance the idea of invisible 

 membrane, but is generally ascribed to vital force. It has not been explained, 

 as far as we have seen, how this membrane is renewed annually in the cambium, 

 and not a continuation of the same ; nor do we see how the transformation of 

 leaves into fiov/ers can be accounted for, if all the organs are originally found 

 in the embryo in a determinate form. To a certain extent the doctrine is true, 

 as parts are found formed long before they are developed. In the Library of 

 Useful Knowledge, it is said the rudiments of the flower have been discovered 

 in the bud seven years before flowering. In hybridising grey peas with white, 

 Mr. Knight observed the transformation only to be partial the first year, and 

 fully developed the next; indeed hybridisation of any kind seems to be against 

 the doctrine. Undoubtedly, at least, it vitiates that part of it which has been 

 carried so far as to attribute the formation of all the plants of a species to 

 exist in the primary germ. We are apt to lose ourselves, however, when we 

 attempt to talk of invisible things. 



