230 PEOF. ATTFIELD PHYSICS AND CHEMISTET 



themselves we as yet know nothing. But chemists discover fresh 

 links every month, and chemistry is revealing to her students some 

 hints as to the manner in which they are joined. So that man's 

 information on these matters is increasing year by year, and what 

 is revealed gives great encouragement to further research. 



More fascinating, possibly, than the study of the chemistry of 

 plant-growth, either from the analytical or from the synthetical 

 points of view, is the study of the natural philosophy, as it used to 

 be termed, or physics or true science of the subject ; that is to say, 

 the study of the cause of the various effects, or a consideration of 

 the explanation of the effects. Bring a log of wood and air together 

 under proper conditions and heat is evolved. Let the vapours and 

 solids resulting from such a combustion be brought together again 

 under proper conditions and wood is reproduced, but one of the in- 

 dispensable conditions here is that heat must be absorbed, the sun 

 must shine on the leaves of the tree producing the wood. "What 

 happens to the heat that is absorbed before it again shows itself 

 when the log is, in the grate, once more resolved into its elements ? 

 Does it lie dormant in the wood, latent, and for the time useless ? 

 Matter is always in motion ; surely force is never quiescent. Neither 

 matter nor force can suffer destruction, but each is ever altering 

 its form. It is certain that the elements of which wood is formed 

 are undergoing ceaseless alteration during the growth of the wood 

 before combustion re-converts the wood into those elements ; it is 

 equally certain that the heat which is absorbed by plants is doing 

 ceaseless work before it reappears as heat when the combustion 

 takes place. Nothing in nature is useless, nothing in nature is still. 



The chemistry and the physics of plant-life at no time more 

 forcibly and unitedly arrest the attention than when one considers 

 the character of the watery fluid or sap of plants, what it is, its 

 functions, and how it performs those functions. For in the sap of 

 the plant-cells the water itself and the mineral matters brought up 

 from the roots, and the gases brought in fi^om the air, meet and 

 unite. In the sap is commenced the structure which when per- 

 fected forms the leaf, the flower, the fruit, the whole edifice of 

 usefulness and beauty. 



Now, knowing something of chemistry and of physics myself, 

 and having never lost my love for botany since the pleasant days 

 of my studentship in that science some thirty years ago, under my 

 present colleague Eobert Bentley, I recently felt my interest in sap 

 strongly aroused by the sight of some literally raining on me from 

 a wounded tree growing in my own garden at Watford. 



On the evening of the 3rd of April, beneath a white birch I 

 noticed a very wet place on the gravel path, the water of which 

 was obviously being fed by the cut extremity of a branch of the 

 birch about an inch in diameter and some ten feet from the ground. 

 I afterwards found that exactly fifteen days previously, namely, on 

 March 19th, circumstances rendered necessary the removal of the 

 portion of the bough which hung over the path, 4 or 5 feet being 

 still left on the tree. The water or sap was di'opping fast from the 



