[74] “Retro”-differentiation, of course, is not “Re”-differentiation (“Umdifferenzierung,” see p. [111]), though it may help it to occur.
[75] Of course such a real decay of parts may happen in other cases.
[76] Certain cases of retro-differentiation occurring under conditions of strict fasting will be described in a later chapter.
[77] Klebs has suppressed the reproductive phase of organisation altogether, in fungi as well as in flowering plants, or has made it occur abnormally early, merely by changing the “external conditions” and by altering the “internal” ones correspondingly. There is hardly anything like an adaptation in these cases, which, by the way, offer certain difficulties to analysis, as the boundaries between “cause” and “means” are not very sharp here.
[78] Compare Herbst, Biol. Centralbl. 15, 1895; and Detto, Die Theorie der direkten Anpassung, Jena, 1904. A full account of the literature will be found in these papers.
[79] Vöchting (Jahrb. wiss. Bot. 34, 1899) forced the bulbs of plants to become parts of the stem, and parts of the stem to form bulbs; in both cases the most characteristic changes in histology could be observed, being in part adaptations, but in part restitutions of the proper type. (See also my Organische Regulationen, 1901, p. 84.) A true and simple instance of a “secondary adaptation” seems to be furnished in a case described by Boirivant. In Robinia all the leaflets of a leaf-stalk were cut off: the leaf-stalk itself then changed its structure in order to assist assimilation, and also formed real stomata.
[80] Arch. Entw. Mech. 17, 1904.
[81] Roux, Gesammelte Abhandlungen, vol. i. 1895; in particular, Der Kampf der Teile im Organismus, Leipzig, 1881.
[82] Arch. Entw. Mech. 21, 1906. By a very detailed comparative study Babák was able to prove that it is the plant proteids to which the effect of vegetable food is chiefly due; thus we have an adaptation to digestibility. Mechanical circumstances are only of secondary importance. (See also Yung.)
[83] Atrophy of muscles by inactivity is not to be confused with atrophy by cutting the motor nerve; the latter is very much more complete.