THE PROBLEMS OF HEREDITY AND THETR SOLTTTIf)N. fyiM 



laws !uk1 thut tho same Lnv should not apply to all characters alike i.s 

 exactly Avhat we have every right to expect. It will also ])o reinem- 

 ])ere(l that the principle is only explicitly declared to apply to discon- 

 tinuous characters." As stated also, it can only l)e true where 

 reciprocal crossings lead to the same result. Moreover, it can oidy he 

 tested when thei'e is no scMisiblt^ diminution in fertility on crossing. 



I'^pon lh(^ appearance of de \'ries's paper announcing Ihe •"redis- 

 covery" and conlii'mation of ^lendeFs law and its extension to a great 

 numl)er of cases, two other observers came forward almost sinudtane- 

 ously and indi^pendently described series of exp(M"iments fully conlirm- 

 ing Mendel's work. Of these pap(n's th(^ iirst is that of Correns, who 

 repeated Mendel's original experiment with pease having seeds of dif- 

 ferent colors. The second is a long and \ery \alu;d)le memoir of 

 Tschermak, Avhich gives an account of elaborate researches into the 

 results of crossing a number of varieties of Pi^urn xiitiruin. These 

 experiments were in many cases carried out on a large scale, and prove 

 the main fact emmciated ))v Mendel bevond an}' possibility of con- 

 tradiction. The more exhaustive of these researches are those of 

 Tsch(n-mak on peas and correns on several varieties of mai/e. lk)th 

 these elaborate investigations have abundantly pro\'ed the general 

 applicability of Mendel's law to the chai'acter of the plants studied, 

 though both indicate some few exceptions. Th(> details of de Vries's 

 experiments are promised in the second \olume of his most \'aluable 

 JfutattonxfJiro/'!, . Corrims in regard to maize and Tschermak in the 

 case of ]\ x(it!rHiii have obtained further proof that Mendel's law 

 holds as well in the case of varieties ditt'ering from each other in two 

 pairs of characters, one of each pair being donnnant, though of course 

 a more complicated expression is needed in such cases.'' 



That we are in the })res(Mice of a new principle of the highest impor- 

 tance is manifest. To v;hat further conclusions it may lead us can not 

 yet be foretold. But ])()th IVIendel and the authors who ]ia\(' followed 

 him lay stress on one conclusion, which will at once suggest itself to 

 anyone who reliects on the facts. For it will be seen that the results 

 are sucli as we might expect if it be imagined that th(^ cross-bred plant 

 produced pollen grains and egg cells, each t)f which bears only one of 

 the alternative varietal characters and not both. If this were so, and 

 if on an average the same i\und)er of pollen grains and Q\f;\y cells trans- 

 mit each of the two characters, it is clear that on a random assortment 

 of ^pollen grains and Qg^ cells Mendel's law would l)e obeyed. For 25 

 per cent of ''dominant" pollen grains would unite with 25 per cent 



« See later. 



''Twherniak's investigations were Ix'sides directed to a reexamination of tlie cjues- 

 tion of the al)sence of beneficial results on cross-fertilizintr 1'. i<alivuiii, a suljject 

 already much investigated by Darwin, and ni)on this matter also in4)ortant lui-ther 

 evidence is give\i in great detail. 



