[258] In plants also reversion forms show sterility in different degrees. Mr. Darwin has called my attention to the fact that the peloric (symmetrical) flowers which occasionally appear as atavistic forms in _Corydalis solida_ are partly sterile and partly fertile. That in other causes of sterility, and above all by bastardizing, the reproductive power is lost in the most varying degrees, has been known since the celebrated observations of Kölreuter and Gärtner. [Eng. ed. An Orchid (_Catasetum tridentatum_) has the sexes separate, and the male flowers (_Myanthus barbatus_) differ considerably from the female (_Monachanthus viridis_); besides these, there occurs a form with bisexual flowers which must be considered as a reversion (_Cat. tridentatum_) and _this is always sterile_. Darwin, “Fertilization of Orchids,” 2nd ed. p. 199.] [259] As we do not know the origin of the “Paris Axolotl” I must restrict myself in the following remarks to _Siredon Mexicanus_ (Shaw). [260] Mühlenpfordt, “Versuch einer getreuen Schilderung der Republik Mejico,” Hanover, 1844, vol. ii. p. 252. [261] [The specific gravity of sea water (Atlantic), according to the determinations of Mr. Buchanan on board the “Challenger,” at 15.56° C. varies from 1.0278 to 1.0240. That of the water of the Dead Sea is 1.17205.--Watts’ “Dict. of Chemistry,” vol. v., table, p. 1017. R.M.] [262] _Loc. cit._ p. 252. [263] “Über die specifische Verschiedenheit des gefleckten und des schwarzen Erdsalamanders oder Molchs, und der höchst merkwürdigen, ganz eigenthümlichen Fortpflanzungsweise des Letzteren.” Isis, Jahrg. 1833, p. 527. [264] The experiments referred to have not been made known; I am indebted for them to a written communication kindly furnished by an esteemed colleague. [265] See Mühlenpfordt’s work already quoted, vol. i. [266] In the province of botany such a case has already been made known by Fritz Müller (Botan. Zeitung, 1869, p. 226; 1870, p. 149). I may be here permitted to quote a passage from the letter in which Dr. Müller calls attention to this interesting discovery. “As a proof of the possibility that a reversion form can again become a persistent character in a species or in the allied form of a particular district, I may refer you to an _Epidendrum_ of the island of Santa Catharina. In all Orchids (with the exception of _Cypripedium_) only one anther is developed; in very rare cases well-formed anthers appear as reversions among the aborted lateral anthers of the inner whorl. In the _Epidendrum_ mentioned, these are however _always present_.”