[8] This is a case of a somewhat different order and I mention it partly for that reason as an illustration of the complexity which such negative instances may present. The difficulty is that though the buffalo and the zebu can breed together, the foetus is too large to be born alive. (See Ackermann _Ber. d. Ver. f. Naturk._, Kassel, 1898, p. 69. Prof. S. Nathusius, of Halle, who has great experience in crossing Bovidae, tells me that he has always failed to cross the buffalo with other species.) [9] In a paper to be published in the Report of the Genetic Conference, Paris, 1911, Bellair states that he obtained some partially fertile hybrids in the cross _N. sylvestris_ × _tabacum_. As to the various degrees of sterility in hybrids between _Nicotiana_ species see Lock, R. H., _Ann. Roy. Bot. Gardens_. Peradeniya, IV, 1909, p. 195. [10] _Beitrage zur Biol. der Pflanzen._, X, 1911, p. 379. [11] One very peculiar feature was observed, namely, that all the new forms in F_{2} which were bred from came true. As I understand, this statement applied to five such new types, and they were represented by 76 individuals in F_{3}, but further details on this point are desirable. Another curious fact was observed, namely that one of the F_{1} forms (_cochleata_ × _radiata_) when fertilised by _cochleata_ gave a highly polymorphic family, but fertilised by _radiata_ the resulting offspring were almost uniform. [12] I also had a few F_{1} seeds given me by Mr. R. H. Lock. [13] In a paper about to appear in _Jour. Linn. Soc._ Mr. A. W. Sutton identifies this Palestine pea as _Pisum humile_ of Boissier and Noé. [14] Lloyd, R. E., _The Growth of Groups in the Animal Kingdom_, London, 1912. INDEX OF SUBJECTS