THE ORIGIN OF FRUITS. 599 



immense difference between a self-conscious, self-guiding organism, and 

 a dead machine requiring to be supplied and regulated by an external 

 consciousness ; yet in the fundamental physical necessity for energetic 

 material, either as food or as fuel, both mechanisms follow essentially 

 the self-same mechanical laws. 



But what has all this to do with the origin of fruits ? Very little at 

 first sight, indeed, yet everything when we look at the bottom of the 

 question. In fact, what is thus true of animals and steam-engines is 

 equally true of plants. No motion can take place in a growing shoot 

 without the aid of solar energy, directly supplied by the sunshine, or 

 indirectly laid by in the older tissues. In the green parts of a plant 

 this energy is immediately derived from the bounteous light which 

 bathes and vivifies the leaves on every side ; but in many other por- 

 tions of the vegetable organism, energies previously accumulated by 

 older organs are perpetually being utilized, for the production of move- 

 ment and growth, by lazy structures which cannot work for themselves, 

 and so feed upon the useful materials collected for them by more in- 

 dustrious members of the plant-commonwealth. Especially is this the 

 case with those expensive organs which are concerned in perpetuating 

 the species to future generations. A flower or a seed cannot directly 

 transform waves of light into chemical separation of atoms ; they de- 

 pend for their growth and the due performance of their important 

 functions upon similar separations already carried on for their behoof 

 by the green leaves on whose bounty they rely for proper subsistence. 

 Carbon, set free from oxygen in the leaves, has been carried to them 

 in loose combinations by the sap ; and as the bud unfolds or the seed 

 germinates, the oxygen once more unites with this carbon (just as it 

 unites in the furnace of the steam-engine, or the recesses of the animal 

 body), and motion is thereby rendered possible. But without such an 

 access of free oxygen to recombine with the energetic materials, the # 

 blossom or the embryo could never grow at all. So we may regard 

 these portions of a plant, incapable of self-support, and dependent for 

 their due function upon energetic compounds laid by elsewhere, as the 

 exact analogues of the animal or the steam-engine. They are in fact 

 similar mechanisms, where food is being used up, and fuel is being con- 

 sumed ; and we find accordingly, as we might naturally expect, not 

 only that motion results, but also that heat is evolved in quantities 

 quite sufficient to be measured by very delicate thermometers. 



Now, every growing portion of a plant shares, more or less, in this 

 animal function of feeding upon previously-fabricated nutriment. But 

 there are two sets of organs, both intended ultimately to subserve the 

 same purpose, in which that function becomes especially apparent. 

 The first is in the case of the whole regular reproductive mechanism, 

 including in that term buds, flowers, fruits, and seeds ; the second is in 

 the case of such subsidiary reproductive devices as tubers, rhizomes, 

 corms, and all the other varieties of underground stems or roots, which 



