230 



The Journal of Heredity 



Continuing the above, he says, "Yet at 

 the same time, one needs indeed pay 

 less attention to differences based on 

 artificial generic characters. Genera 

 like Pi sum and Vicia, Ervum and Vicia, 

 Lychnia and Cucubalus, are in their na- 

 ture so related that hybrids can arise 

 from them, as Koelreuter and I have 

 demonstrated" (p. 27). "So much the 

 more I dispute his opinion," he says 

 of Koelreuter (p. 25), "respecting the 

 falsely derived difference between true 

 ' species ' and 'variety ' from the fertility 

 or infertility of the hybrid plants." 



CHANCE CROSSING IN NATURE 



Wiegmann in fact regards chance 

 crossing in nature, between species or 

 sorts of plants, as having given rise to 

 new agricultural races. "It appears 

 from my experiments," he says (p. 26), 

 "that many species, or constant sub- 

 species, e. g., Pisuni arvense, Vicia 

 leucosperma, Vicia faba (red-seeded), 

 as well as the most of the varieties of 

 cabbage and the cereals, whose origin is 

 unknown, possibly are hybrid plants, 

 which have been produced upon our 

 fields and in our gardens, through the 

 proximity of a few related plants, and 

 which have remained constant." 



Wiegmann sums up the matter of the 

 bearing of degree of relationship upon 

 crossing as follows (p. 27): "Mainly 

 it comes to the point that the differ- 

 ent plants do not vary from one another 

 greatly in their natural constitution, 

 and that their secretions are not too 

 heterogeneous, since otherwise the pol- 

 linating substance would not be ab- 

 sorbed by the stigma. "In general," 

 he says, "foreign pollen takes hold of 

 the stigma with much greater difficulty 

 than does its own, and in order to obtain 

 complete fertilization, one must often 

 deposit it several times, even when the 

 foreign pollen is from a > plant of the 

 same species" (p. 3). 



Wiegmann 's experiments covered a 

 list of thirty-six crosses, using the fol- 

 lowing species and cultivated varieties: 



Allium (onion, etc.), 2 species. 



Brassica (cabbage, etc.), 4 race- 

 species. 



Dianthus (pink), 3 species. 



Ervum (lentil), 1 species. 



Nicotiana (tobacco, etc.), 2 species. 



Phaseolus (bean), 2 varieties. 



Pisum (pea), 2 species. 



Vicia (vetch), 1 species. 



The general conclusions Wiegmann 

 draws from his experiments are most 

 interesting. The most important are 

 those which relate to the possible vigor 

 of new species (p. 3) : . . . "My ex- 

 periments sufficiently prove," he says, 

 "that the fertilization of different sub- 

 species, inter se, is ^ source of manifold 

 rvmning-out of species in the plant 

 kingdom, and that insects, especially 

 bees and humblebees, as well as little 

 beetles and flies, play a much more im- 

 portant role in the fertilization of plants 

 than one has lately been inclined to 

 allow them, but of which I have the most 

 indubitable proofs." 



"Even though the structure of the 

 corolla in the case of leguminous plants," 

 he says again (p. 26), "scarcely appears 

 to admit of the access of insects and 

 foreign pollen, yet the plants obtained 

 from the seed of experimental plants 

 show such a striking alteration in their 

 specific characters, especially in the 

 form of the seed and its envelopes, 

 that an influence of foreign pollen on 

 the ovules will scarcely be able to be 

 denied. I myself have numberless 

 times convinced myself of the fact 

 that humblebees, bees and small in- 

 sects from the orders of flies and beetles, 

 can fertilize the flowers of the Legum- 

 inosae in the manner stated by Sprengel. 

 It is therefore necessary in agriculture to 

 give heed to this matter, if one wishes 

 to keep plants that are to be cultivated, 

 in their quality and integrity." 



With respect to observations of a 

 more special nature, Wiegmann 's mem- 

 oir contains much of interest. Re- 

 garding the breaking up of the progeny 

 of hybrids, he says, speaking of Koel- 

 reuter's observations: "I have found 

 his observation well founded, that the 

 plants produced from one seed and 

 from one capsule of hybrid plants 

 often differ from one another in respect 

 to fertility, and especially in the struc- 



