FUNCTION OF AZOTISED MATTER IN PERENNIALS. 61 



being formed into leaves, stems, and root-fibres, or 

 finally into seed. The soluble constituents of a bud, a 

 tuber, or the root of a perennial plant, are identical 

 with the seed constituents. The cereal plant produces 

 azotised and unazotised substances in the same propor- 

 tion as in the albumen (farinaceous body). The potato 

 plant produces the constituents of the tuber, which are 

 formed into leaves and branches or roots ; or, if the ex- 

 ternal conditions are no longer favourable to the forma- 

 tion of leaves and roots, accumulate again in the under- 

 ground stem, to form new tubers.* 



While the growth of the plant continues, the first as 

 well as the last leaves and roots will, with a proper 

 supply of food, maintain their existence, since they re- 

 produce out of the nutriment supplied to them the 

 identical constituents from which they themselves arose. 

 The excess of these, which they do not require for their 

 own enlargement, goes to those parts of the plant where 

 the motion of the fluids or the cell-formation is most 

 active, viz., to the roots, the leaf-buds, or the extreme 

 points of the roots and shoots ; and, finally, as in the 

 case of summer plants, to the organs of seed-formation 

 which at the ripening of the seed absorb most of the 

 movable seed-constituents existing in the plant. 



The supply of the incombustible elements of food 

 led to the formation of unazotised matter, a portion of 

 which was used to form woody tissue, whilst another por- 

 tion remained available for the same purpose. The supply 

 of nitrogenous food caused a corresponding production 

 of nitrogenous matter, so that the protoplasm was con- 

 stantly renewed, and, so long as the chemical process 

 lasted, was increased. 



* Boussingault has observed that even seeds weighing two or three 

 milligrammes, sown in an absolutely sterile soil, will produce plants in 

 which all the organs are developed, but their weight, after months, does 

 not amount to much more than that of the original seed, even if they 

 vegetate in the open air ; and the result is more marked if they grow in a 

 confined atmosphere. The plants remain delicate, and appear reduced in 

 all dimensions; they may, however, grow, flower, and even bear seed 

 which only requires a fertile soil to produce again a plant of the natural 

 size. (* Compt. rend.' t. xliv. p. 940.) 



