THE PROBLEMS OF HEREDITY AND THEIR SOLUTION. 563 



|)ut)lisli(Ml ;i ])riet' account" of experiincnts which he lias for several 

 years been carrying on,- giving' results of the highest value. . 



The description is A'er3',>short, and there are several points as to which 

 more precise information is necessary, both as to details of procedure 

 and as to statement of results. Nevertheless, it is impossil)le to dou])t 

 that the work as a whole constitutes a marked step forward, and the full 

 })ublication which is promised will ])e awaited with great interest. 



The work ndates to the course of heredity in cases where dotinite 

 varieties ditiering fi'om each other in some one detinite character are 

 crossed together. The cases are all examples of discontimious varia- 

 tion — that is to say. cas(>s in which actual intermediates l)etween the 

 parent forms are iiot usually produced on crossing.'' It is shown that 

 the subsequent posterity ol)tained ]}y self -fertilizing these crossbreds 

 or hyl)rids, or by breeding them with each other, break up into the 

 original i)arent fornis according to fixed numerical rule. 



Professor de Vries begins by reference to a remarkable miMuoir by 

 (iregor ^lendel.' giving the results of his experiments in crossing 

 varieties of /Vsv//// s(/f//u///i. These experiments of MendeFswere car- 

 ried out on a large scale, his account of them is excellent and complete, 

 and the })rinciples which he was a})le to deduce from them will cer- 

 tainly play a conspicuous })art in all future discussions of evolutionary 

 ])r<)hlems. It is not a little remarka])le that MendeFs work should 

 have escaped notice and been so long forgotten. 



For the purposes of his experiments Mendel selected seven ])airs of 

 characters, as follows: 



1. Shape of ripe seed, whether round or angular and wrinkled. 



2. Color of ' ' endosperm " (coty ledonsj, whether some shade of yellow 

 or a more or less intense green. 



3. Color of the seed skin, whether various shades of gray and gray- 

 brown or white. 



4. Shape of seed pod, whether simply inHattnl oi- deeply constricted 

 l)etween the seeds. 



5. Color of unripe jxhI, whether a shade of green or hi'ight yellow. 

 (>. Nature of inflorescence, whether the flowers are arranged along 



the axis of the plant or nvv terminal and form a kind of uml)el. 



7. Length of stem, whether al)out <> or 7 feet long or about three- 

 fourths to li feet. 



Large numbers of crosses were made between pease ditiering in 

 respect of one of each of th(\se paii's of characters. It was found that 

 in each case the otfspring of the cross exhi])ited the character of one of 

 the parents in almost undiminished intensity, and intermediates which 



«C()mptes RenduH, Marcli L'(i, l!i()(), and 7k>r. d. Deutscli. Bot. Ccs., XVITT, 1900, 

 p. 83. 



''This conccptiou of (lii-<c<)utiniiity i.s, of courwe, pre-Mendcliuii. 



f-' "Yersuche lib. .Pflanzenhydrideu" in the Verh. d. Naturf. Wt, Ijiuiiu, IV, l.Sfio. 



