7o6 CHEMICAL PROCESSES JN THE PLANT. 



phyll ; it is only in the presence of this substance that elimination of oxygen, 

 and therefore assimilation, can take place. In the case of a long series of other 

 substances, many colouring matters, acids, alkaloids, wax, tannin, pectinaceous sub- 

 stances, &c., no relation to the other processes of metastasis is known, nor any 

 physiological signification which they possess in the life of the plant. 



In some cases substances which have ceased to take part in the processes of 

 growth and of metastasis are nevertheless important or even indispensable for other 

 purposes of vegetation. Of this class are the saccharine juices secreted by nec- 

 taries, which are of service to the plant only so far as they attract insects which thus 

 bring about the conveyance of the pollen to the stigma. For a similar purpose a 

 portion of the tissue of the anthers of Orchids is transformed into a viscid glutinous 

 substance by which the pollinia become attached to the proboscis of insects. Thus 

 again the sapid and nutritious substances which constitute the pericarps of some 

 fruits are of no direct use for the growth of the seeds, but cause their dissemi- 

 nation by animals which feed on the fruits and thus disperse the seeds. 



We must now again turn, after this preliminary explanation of the various parts 

 ■played by the products of metastasis in the life of the plant, to the most important 

 group of organic compounds, those which have been distinguished above as form- 

 ative materials. 



The determination whether any chemical compound belongs to the class of 

 formative materials of the cell-wall and protoplasmic substances depends on its 

 behaviour during growth, on its chemical composition, on its appearance and dis- 

 appearance in growing cells and tissues, and on its chemical relations to other 

 substances, especially to cellulose and to protoplasmic substances. Spores, seeds, 

 bulbs, tubers, rhizomes, the persistent parts of woody plants, and other reservoirs 

 of reserve-material, always contain chemical compounds belonging to two different 

 groups. On the one hand nitrogenous substances are always present in the form 

 of albuminoids (often several different ones as in the grains of cereals) which 

 scarcely differ chemically from protoplasm, and when contained in the succulent 

 reservoirs of reserve-materials preserve even the form of protoplasm. From this 

 similarity, and still more when the migration and other relations of these sub- 

 stances are kept in view, the conclusion must be drawn that we have in them 

 the material for the formation of protoplasm in the newly-formed organs. On 

 the other hand all these reservoirs of reserve-material contain one or more non- 

 nitrogenous substances belonging to the series of carbo-hydrates and oils. In 

 seeds and spores there is generally a great deal of oily matter and little or no 

 starch ; but many seeds contain on the other hand a great deal of starch with but 

 little oily matter. In tubers, many bulbs, rhizomes, and stems, there is usually much 

 starch stored up with but little oily matter ; while in some tubers (as the Dahlia, Arti- 

 choke, &c.), the starch is replaced by inulin; in the bulbs of Allium Cepa by*a sub- 

 stance resembling grape-sugar ; in the root of the Beet by crystallisable cane-sugar. 

 Small admixtures of oily matter appear to be never absent, and in some cases, 

 especially in many seeds, this alone is present without any carbo-hydrate (as the 

 Almond, Gourd, Castor-oil plant, &c.). 



Together with albuminoids, carbo-hydrates, and oils, a variety of other com- 

 pounds may also occur in the reservoirs of reserve-material ; but the limitation of 



