. An introduction to vegetable physiology. Plant physiology. METABOLISM 275 bye-products of metabolism is not at all well defined. In many cases substances are included in the latter category because nothing is known as to their function, and the classification can therefore be regarded only as provisional. In many cases it cannot yet be determined whether particular substances are formed by the direct decomposi- tion of protoplasm, or by subsequent changes in the primary products of such decomposition. Till quite recently the formation of resin and allied bodies in the resin passages of the C
. An introduction to vegetable physiology. Plant physiology. METABOLISM 275 bye-products of metabolism is not at all well defined. In many cases substances are included in the latter category because nothing is known as to their function, and the classification can therefore be regarded only as provisional. In many cases it cannot yet be determined whether particular substances are formed by the direct decomposi- tion of protoplasm, or by subsequent changes in the primary products of such decomposition. Till quite recently the formation of resin and allied bodies in the resin passages of the Conifers and in many glandular hairs was con- sidered a true secretion, the aromatic substances being held. Fig. 124.—Glandular Haiks i'bom Primula sinensis. u, young hair; b, haii' showing secre- tion formed in the cell-wall of the terminal cell; c, hair after discharge of the . Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Green, J. Reynolds (Joseph Reynolds), 1848-1914. London, J. & A. Churchill
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