7o6 
CHEMICAL PROCESSES IN THE PLANT. 
phyll ; it is only in the presence of this substance that ehmination 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 tlTus 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 dififerent 
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 
litde oily matter. In tubers, many bulbs, rhizomes, and stems, there is usually much 
starch stored up with but litde 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 comr 
pounds may also occur in the reservoirs of reserve-material; but the limitation of 
