230 Atkinson. 



stem, and pycnocarpa in the cutness of (rosette) leaves. They are not 

 intermediates in the sense that one hybrid resembles one parent modi- 

 fied by the constitution of the other as in laeta and velutina, but are 

 mosaics formed by a recombination of the characters of the parents. 

 The real intermediate hybrid is nutella- in which the vegetative char- 

 acters are blended very much according to the usual type in many 

 species crosses. In mutation crosses, according de Vries, there is a 

 splitting of the entire constitution (gametic) so that all the vegetative 

 characters are split, not sorted as in pycnella and tortuosa^). The pro- 

 duction of the twin segregate hybrids (pycnella and tortuosa) and the 

 blend (? triplet) hybrid {nutella) in the first generation of crosses bet- 

 ween these two wild species appears to be of a different type from the 

 production of twin hybrids in mutation crosses. The twin segregates 

 {pycnella and tortuosa) are also of a very different type from the twin 

 hybrids obtained from the cross, wild grandiflora X american "hietmis" 

 by Davis (1. c. 1910), since many characters of the parents dominate 

 in the one or the other segregate, but different characters from the 

 two parents dominate in each of the hybrids. 



The three different hybrid types (twins and triplet) in the Fi 

 generation of crosses between Oe. pycnocarpa and Oe. nutans differ from 

 the mutation crosses described by de Yries in another respect. In the 

 mutation crosses triplets are formed only when the mutant parent is 

 an inconstant race, for example Oe. lata which is pure female. The 

 pollen of Oe. lata is sterile, except in certain lata forms derived by 

 splitting in the first generation of a cross. When Oe. lata is pollinated 

 with Oe. hookeri, cockerelli, biennis Chicago etc., the splitting in the first 

 generation produces the twins laeta and velutina, and in addition a third 

 form which is lata repeated, but slightly modified. The most common 

 modified form of this lata arising by splitting in the first generation of 

 a cross shows a resemblance to laeta forms and is called lata -laeta. 

 This is the "triplet". Very often a fourth form also appears (qua- 

 druplet) which is the lata with velutina characters {lata -velutina). 

 Triplets and quadruplets in mutation crosses are only known to appear 

 when one of the parents is an inconstant race, and besides the splitting 

 in the Fi generation into twins, laeta and velutina, the inconstant race 



^) The "mosaics" presented by the twin segregates {pycnella and ioriuosa) are 

 of a diflFerent nature from that described by Blaringhem (107, 1913) in F^ generations 

 between different species of barley. 



