348 PLANT HYBRIDIZATION BEFORE MENDEL 



experiments on a larger scale and with greater exactness. (zT?., 

 p. 232.) 



The central point of the paper, so far as the Mendelian dis- 

 cussion is concerned, follows : 



"l also carried out artificial crosses between different varieties of 

 Pisum sativum, which had as the objective the study of the immediate 

 influence of the foreign pollen upon the constitution (form and color) 

 of the seeds produced thereby, as well as to follow in the following 

 generations of the hybrids the inheritance of constant differing charac- 

 ters of the two parent sorts used for crossing. 



"In the second year of the experiment, the behavior of the hybrids 

 in respect to their growth (especially with respect to their height), their 

 seed-production, and the change in color and form of the seeds and 

 pods, when placed in comparison with the corresponding characters of 

 the descendants obtained from self-fertilizati(;n of the parents." (ib., 



P- 233.) .... 



"On nine different varieties of peas, crosses were carried out between 



flowers of the same plant (geitonogamy), between flowers of the same 

 variety but of other individuals (isomorphic xenogamy), and between 

 flowers of different varieties, the seeds of which are distinguished from 

 one another either through their form, or color, or through both char- 

 acters (heteromorphic xenogamy)." (pp. 233-4.) 



The results of the experimental work then briefly follow (ib., 

 pp. 234-9) ■ 



The crossing-for-height experiment contirmed Darwin's results, 

 so far as the comparison of self-fertilized plants with geitonoga- 

 mous crosses was concerned. With respect, however, to crosses in 

 the ordinary sense (heteromorphic xenogamy), i.e., those between 

 varieties called by the author "Mischlinge" (hybrids), only cer- 

 tain of the hybrid forms showed Increased growth in height over 

 the selfed plants. 



"with other combinations, on the other hand, such an 'advantage' of 

 crossing as against self-fertilization was lacking, and a plus increment 

 of the hybrid as compared with the self-fertilized maternal variety, for 

 example in the case of a hybrid from a relatively dwarf variety, with a 

 relatively tall one, is primarily indeed simply to be taken as an inheri- 

 tance from the father, and is not to signify an 'advantage' from crossing 

 per se in contrast to self-fertilizaticm. 



"For an interpretation in the latter sense, only such cases are justifi- 

 able in which the hybrid exceeds in height the derivations of self- 

 fertilization not only of the maternal variety, but also of the paternal 

 one." (ib., p. 234.) 



There follows hereupon the statement of the significant results 

 of von Tschermak's own experiments, so far as F^ dominance is 

 concerned : 



