This phenomenon, which we have termed "exogamy," is common in Protophyta; it has been clearly demonstrated by Schaudinn in Foraminifera and the Lobose Rhizopod Trichosphaerium (p. [53] f. Fig. 9), and by Pringsheim in the Volvocine Pandorina (p. [128] f. Fig. 45). It is quite independent of the differentiation of binary sex.
Other modes of syngamy, such as karyogamy and plastogamy, we shall discuss below, pp. [69], [148]; see also p. [30].
See Gruber in Biol. Centralb. iv. p. 710, v. p. 137 (1884-6), in Ber. Ges. Freiburg, i. ii. 1886-7; Verworn (reference on p. 16); F. R. Lillie in Journ. Morph. xii. 1896, p. 239; Nussbaum in Arch. mikr. Anat. xxvi. 1886, p. 485; Balbiani in Recueil Zool. Suisse, v. 1888, in Zool. Anz. 1891, pp. 312, 323, in Arch. Microgr. iv. v. 1892-3. For Higher Organisms especially see T. H. Morgan, Regeneration, 1901.
Whence the antiseptic powers of such aromatic alcohols as phenol and thymol, and acids as salicylic acid, etc., and their salts and esters.
The portion of the spectrum that is operative in "holophytic" nutrition is the red or less refrangible half, and notably those rays in the true red, which are absorbed by the green pigment chlorophyll, and so give a dark band in the red of its absorption spectrum. The more refrangible half of the spectrum, so active on silver salts, that it is usually said to consist of "chemical rays," is not only inoperative, but has a destructive action on the pigments themselves, and even on the protoplasm. Chlorophyll is present in all cases even when more or less modified or masked by the accompaniment of other pigments.