FOOD OF PLANTS. 555 



produced r the cellulose of the cell-wall, now no longer required for 

 the purposes of the individual cell, the contents of which, however, 

 proceed with their assimilative action. After a time the cell prepares for 

 propagation, or reproduction. Then the starch-granules disappear, 

 apparently by solution, into dextrinous or analogous matter requisite 

 for the development of new cell-membrane, which soon takes place, 

 either in cell-division (p. 451), or, if the primordial utricle is dis- 

 charged from the parent cell in the form of zoospores (p. 451), in the 

 formation of the cell-membranes of these bodies after they have come to 

 rest. 



Where resting-spores are to be formed, different changes ensue after 

 the solution of the accumulated starch. The new cell, intended to remain 

 in a quiescent condition, becomes coated by a cellulose membrane, or often 

 two distinct concentric coats ; and, at the same time, that portion of the 

 contents consisting of dextrinous or analogous matter which has not been 

 consumed in forming cell-membrane becomes converted into Jived oil, the 

 green colour disappears, and the contents assume a red or brown colour, 

 and external stimuli (light, &c.) produce no influence. When these 

 bodies germinate (which usually only occurs after they have been dried 

 up and are again placed in water), the chlorophyll gradually reappears 

 and the oil vanishes, and the entire course is run through again. 



Transfer of Stored Nutriment Metastasis. Comparing these phenomena 

 with what we observe in the higher plants, we notice the similarity as re- 

 gards the production of chlorophyll in the leaves, followed by the appearance 

 of starch-granules, as a form of accumulated nutriment. But the functions 

 being more localized as the organization is more complicated, the starch 

 thus formed is subsequently dissolved, and is carried away to the growing 

 tissues of the plant, to the buds, cambium-region, and roots, where it is 

 laid up in autumn, very often in this same form, but not unfrequently in 

 the condition of h'xed oil, as in the rhizomes of Cyperus, of Lastrcea 

 Filix-mas, &c., and, above all, in structures which, like the resting-spores 

 above mentioned, are to remain quiescent while exposed to considerable 

 diversity of external conditions, namely in seeds, as in the cotyledons of 

 Cruciferae, Almonds, Nuts, Walnuts, &c., or in the perisperm of Poppies, 

 Euphorbiaceee, &c. 



The oil (or starch in other cases) stored up in the seeds and rhizomes 

 by metastasis undergoes decomposition and solution in germination, to 

 supply material for the cell-membranes of the nascent plant until the roots 

 have become sufficiently developed to provide for it. 



We have at present no very satisfactory evidence of the kind here 

 brought forward to indicate the mode in which the nitrogenous matters, 

 necessary for the formation of new protoplasm, are taken up. The ques- 

 tion of the assimilation of nitrogenous matters will be considered in the 

 following section, on the Food of Plants. 



Sect. 3. FOOD OF PLANTS. 



Constituents of Plants. The first step in the investigation of 

 this subject is to ascertain what substances enter into the compo- 

 sition of vegetable structures and juices. 



