42 THE PLANT. 



The organic process of cell-formation presupposes the 

 presence of the protoplasm, and is independent of the 

 chemical process by wliich the latter is generated ; but 

 this chemical process is indispensable to the continuance 

 of the cell-formation. 



In a young plant which has been developed in pure 

 water alone, the chemical process must soon come to an 

 end for want of the necessary external conditions. Tlie 

 leaves and roots in this case can do no work as formative 

 organs. In the absence of food they generate no products 

 upon which the continued existence of the plant depends. 

 When they have arrived at a certain state of develope- 

 ment, the ceU-formation ceases in themselves, although it 

 is still continued in the new root-buds and leaf-buds. The 

 latter stand to the movable contents of the previously 

 existing leaves and roots in the same relation as the 

 embryo of the wheat-seed to the farinaceous body. The 

 non-nitrogenous and azotised constituents which represent 

 the working capital of the existing roots and leaves are 

 transformed as these die mto new organs, and new leaves 

 are developed at tlie expense 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 external 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 impaked : 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 nitrogenous substance. 



