56 THE PLANT. 



pense of the constituents of the old ones. But these 

 processes are of short duration ; after a certain number 

 of days the young plant dies. The more immediate ex- 

 ternal cause of its short duration is the want of food ; 

 but another internal cause is the conversion of the non- 

 nitrogenous soluble substances into cellulose or woody 

 tissue, whereby it loses mobility. With the diminution 

 of this soluble substance the most essential condition of 

 cell-formation is impaired : when the whole has been 

 consumed, the process comes to an end. The withered 

 leaves, when burnt, leave behind a certain quantity of 

 ash, showing that they retain some mineral matter ; 

 there remains in them also a small portion of nitroge- 

 nous substance. 



The most remarkable thing in this developement is 

 the part performed by the nitrogenous matter of the 

 seed, which becomes a constituent element of the root- 

 fibres, stems, and leaves, where its agency serves to 

 bring about the formation of cells. After the death of 

 the first leaves, it becomes a constituent of the new 

 ones, performing in them the same part over again, so 

 long as there remains materials for cell-formation. But 

 the nitrogenous matter itself is not in reality worked up 

 in the plant, and forms no actual tissue or component 

 part of the cell. 



The experiments of BOUSSINGAULT on the growth of 

 plants, in the absence of all nitrogenous food (' Annal. 

 de Chim. et de Phys.,' ser. iii., xliii., p. 149), though 

 undertaken for a different purpose, are well adapted to 

 remove all doubt about the very important power pos- 

 sessed by the nitrogenous matter just now alluded to, 

 viz. of mg|intaining the vital process in the plant, even 

 where the mass of the plant itself receives no increase. 



In these experiments lupines, beans, oats, wheat, 

 and cresses were sown in pure pumice-stone dust, washed 

 and burnt, with which was mixed a certain quantity of 

 ash from stable-manure and from seeds similar to those 

 sown. The plants were grown partly under glass bells, 

 with a constantly-renewed supply of air containing car- 

 bonic acid. The air supplied and the water used for 



