IRISH GARDENING 



27 



liow to question nature as to her inmost processes, 

 and studied how to interi)ret her answers. 

 Owing largely to his influence, the teaching of 

 Hotaiiy lias develoi>ed more and more along 

 the lines of plant physiology ; the physical 

 sciences have been Imi^ressed into the service and 

 the rtiiuly of the siihjcct has become more intense 

 iuu\ iiLlcri'stiiiL; iMiisimich as it deals more closely 

 with tlif i»i(ihlciiis aiul activities of life itself, as 

 revealed in the vegetable world around us. 



We have now traced tlie sources from which 

 ])lants draw the materials to build up their 

 substance ; the carbonic acid gas taken in by the 

 leaves from the air, the water taken up by the 



in'ism-sliaped, so as to sjjlit up the beam into it.s 

 component colours, dark bands arc noticed in the 

 red, in the yellow and other colours, showing 

 some of the light has been a1)sorbed. In the leaf 

 the energy of this absorbed light becomes latent 

 in tlie potential energy of the newly -formed 

 starch and sugar. 



The energy is changed by the chlorophyll from 

 one forin into another, from the bright dancing 

 sunbeani to the stored vip energy of starch 

 Beginning with this starch the plant is enabled to 

 build up the various other compounds of which 

 its tissues are composed, to assimilate the nitrogen, 

 the i)hosphorus, the potassium, and all those 



Saxikra(;\ Bii 



<FJ!IAXA AT MULLABt)Di:X. 



(See page 22.) 



[\V. .Mit.liison 



roots, and the comparatively small amount of 

 mineral matter got froni the .soil and taken up in 

 solution. How can the i)lant combine them ? 

 The idea of " vital force " is not adnussible. A 

 ])lant cannot create energy any more than it can 

 create matter, and to conxbine these inorganic 

 materials is like taking water ux> a hill, it means 

 work. Where does the energy come from ? 



Carbon a.ssimilation only takes place in sun- 

 light, and the sun is the great source of energy. 

 As we know the green colouring matter — the 

 chloro])hyll, as it is called — enables the plant to 

 avail of this energy : how it does it we know not; 

 buti this we do know — if a. sunbeam be ]>assed 

 througli a solution of chlorophyll in a glass jar, 



other elements necessary to ils life. The 

 reverse of this building-up pi'ocess takes ]tlace 

 when a log of wood is being hui'iit. Tiie carbon 

 takes up oxvgen and disappears once more into 

 the air. the "water (lisapi)ears as vajKnir, soon to 

 be condensed and so to return to the earth as ram. 

 The ash or mineral matter alone remains. The 

 absorbed sunlight that at the bidding of life had 

 bound them all together now reappears in the 

 form of heat. In the language of the chemist, 

 the organic has given place to the inor- 

 ganic. Nothing is lost, however. All the elements 

 are now ready to lake part in the same cycle over 

 aeain. , . . 



We nuiv conclude our article on carbon assitui- 



