i62 PLANT HYBRIDIZATION BEFORE MENDEL 



have been produced upon our fields and in our gardens through the 

 proximity of a few related plants, and have remained constant." (p. 26.) 



Wiegmann sums up the matter of the bearing of degrees of 

 relationship upon crossing as follows (p. 27) : 



"Mainly it rests on the point that the different plants do not vary 

 from one another greatly in their natural constitution, and that their 

 secretions are not too heterogeneous, since otherwise the pollinating 

 substance would not be absorbed 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 com- 

 plete 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 following species and cultivated varieties : 



Avena, 3 species and varieties Ervum (lentil), 1 species 



Allium (onion, etc.), 2 species Dianthus (pink), 3 species 



Brassica (cabbage, etc.) 4 races Phaseolus (bean), 2 varieties 



Nicotiana (tobacco, etc.), 2 species Verhascum, (mullein), 9 species 



Pisum (pea), 1 species Vicia (vetch), 3 species 



The general conclusions Wiegmann draws from his experi- 

 ments are most interesting. The most important are those which 

 relate to the possible vigor of new species. 



"My experiments sufficiently prove," he says, "that the fertilization of 

 different subspecies, inter se, is a source of manifold degenerations of 

 species in the plant kingdom, and that insects, especially bees and bumble- 

 bees, as well as little beetles and flies, play a much more important role 

 in the fertilization of plants than one has lately been inclined to allow 

 them, but of which I have the indubitable proofs." (p. 3.) 



"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 seeds 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 bumblebees, bees and small insects from the order of flies and 

 beetles, can fertilize the flowers of the Leguminosae 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, Wieg- 

 mann's memoir contains much interest. Regarding the breaking-up 

 of the progeny of hybrids, he says, speaking of K61 renter's obser- 

 vations : 



"I have found his observations well founded, that the plants produced 

 from seed from one capsule of hybrid plants, often differ from one 



