64 

 Crossings between sorts which differ in regard to certain characters. 



When wheat sorts of which the average head density is different have been 

 crossed, it has been found in some cases that extremes, which appear to be 

 quite new forms, arise. An example is given by Nilsson-Ehle (52 p. 279-80) 

 in the crossing of an autumn wheat (Triticum compactum) having a head 

 density of 55, with Grenadier (T. Vulgare) having a head density of 32. In the 

 second generation there were found 10 forms out of a total of 42, having 

 a head density of from 18 to 21. Such heads were of course very long and 

 open and appeared distinctly different from either parent. Conversely, by 

 crossing one of these open-headed individuals with another variety possessing 

 about the same degree of head density, compactum types may be produced. 

 The appearance of such forms is not attributed t so-called ' reversion' or to 

 'mutation' but simply to a peculiar combination of already existing units. 



The fact that head density, or length of the internode in heads, is a Men- 

 delian character is further amplified by Nilsson-Ehle (52 p. 26-56) in con- 

 nection with crossings recently described in detail. In all of these crossings 

 the compact headed T. Compactum (Schwed. Binkelweizen) was one of the 

 parents, the other parents possessing heads of from average to low density. 



One of the most interesting of these crosses was T. Compactum X Pudel 

 (See Figs. X-XII). the latter sort possessing a head of average density. The 

 result of this crossing (in line B.) was as follows : 



F t : Compactum. 



F 2 : Segregating into 61 genuine compactum (of which number 5 were 

 decidedly more compact than either of the parent sorts) ; 5 somewhat 

 more outdrawn-compactum ; 28 of the foregoing group sharply 

 defined as average to more open head than either parent ( = 2.4 

 Compactum: 1 not-compact urn) . 



The seed of all of the 94 F 2 plants was sown out in separate rows 

 with the following results: 



5 compactum: very dense F 3 : 5 constant compactum 



("18 



56 F 3 -j 38 segregating into compactum and 



' not-compactum.' 



5 somewhat more outdrawn compactum F 3 : 5 segregating into com- 

 pactum and ' not-com- 

 pactum.' 



28 'not-compactum' F 3 All the progeny obtained in 



inheritance the " not- 

 compactum " character. 



Of the 23 constant compactum individuals 5 were decidedly more 

 dense than the others. Three of these retained this exceptional density 

 while the other 2 again assumed the average condition of the lot. Of the 

 remaining 18 of the constant compactum individuals, 2 proved especially 

 dense. 



