74 



SOME CONTHIBUTIONS TO PLANT-CHEMISTBr. 



On comparing these numbers with the corresponiling figures re- 

 presenting the centesimal composition of Beech-scales, wo find that 

 they show a far greater richness in the three more precious elements of 

 plant-nutrition. The nitrogen is here five and a half times as much 

 as in the former case, the potash six times as much, and the phos- 

 phorus pentoxide four and a half times as much. I hope on another 

 occasion to secure the data by which an approximative estimate may 

 be made of the relation between tlie weight of the annual produce of 

 Elm-flowers and that of the leaves of this tree. Such an estimate 

 will afford some insight into the scale on which the movements of 

 nutrient materials both within and without the plant must be con- 

 tinually taking place. 



For the analyses included in sections 1 and 11 I am indebted to 

 my pupil, Mr. P. H. Cathcart. 



12. Triticum sativum.' When a grain of Wheat is slightly damped 

 and then carefully peeled, a thin membrane is removed which con- 

 tains three layers of cells firmly united. The two outer layers are 

 greyish in colour, irregular in structure, and consist mainly of cellu- 

 lose aud lignose, but there is a yellowish and decidedly nitrogenous 

 layer adherent to their inner aspect. We may reasonably assume 

 that the whole of these layers, united together as they are (they are 

 indeed inseparable by mechanical means), make up the pericarp of the 

 caryopsis. Now it is a matter of interest to ascertain how far this 

 pericarp differs in chemical composition from the testa and endopleura, 

 with the strongly-adherent outer row of yellow cells of the endosperm, 

 which is always intimately associated with them. Again, we may 

 compare the pericarp with the embryo from a chemical point of view, 

 and it is about this latter comparison that I propose now to offer 

 some observations. 



When perfectly clean specimens of the above-named parts of the 

 Wheat-grain had been secured, their most important constituents were 

 determined to be as follows : — 



Analysis of Wheat-Ghaln. 



100-00 



100-00 



The above analyses, though far from complete, owing to the diffi- 

 culty of obtaining sufficient supplies of the materials in a satisfactory 

 condition of purity, show how very different is the chemical composi- 

 tion of these two structures, and how closely it accords with the 

 offices which they have respectively to discharge. Doubtless cellulose 

 and lignose constituted the main portion of the 70-51 per cent, entered 



