HYBRIDISATION AND WHEAT HYBRIDS 383 



These facts, together with the experimental results of Godron and 

 others, make it clear that the so-called wild " sports " or varieties of 

 A. ovata from which Fabre began his cultivations were natural hybrids, 

 the result of chance fertilisations of A. ovata by pollen of wheat from 

 neighbouring fields. 



Godron found that the first cross is sterile, due to the imperfection of 

 the stamens, but, as discussed later, it yields secondary hybrids with 

 pollen of its male parent (7". vulgare). 



Bally, in 1916 and 1917, made the cross T. vulgare 9 x Aegilops ovata o 

 and obtained 3 F t plants from some 40 pollinations. He succeeded also 

 with the reciprocal cross Atgilops ovata 9 x T. vulgare <$ , obtaining 2 

 F, plants from about 200 pollinations. 



In both cases the hybrids were alike and sterile, and resembled those 

 obtained by Godron and others. The pollen grains varied considerably 

 in size, fluctuating between 20 and 53 /i in diameter ; they were more 

 translucent than those of either parent, and devoid of the fine starch grains 

 seen in the normal pollen grains of wheat and Aegilops. Bally also studied 

 the cytology of the two parents and the hybrid, and found that the haploid 

 number of chromosomes in wheat is 8, that of Aegilops 16. The hybrid 



presumably should have 12 (- j as the haploid number. In some 



cases he found this number present, but in others the number was greater 

 than 12, for during the reduction division some of the Aegilops chromo- 

 somes remained unpaired and divided longitudinally as in the ordinary 

 homotypic mitosis. The wheat chromosomes arc short and thick, those 

 of Aegilops much longer and thinner. In the mciotic division of the 

 hybrid the two parental chromosomes which can be recognised with 

 certainty travel to the poles of the spindle at different rates, the wheat 

 chromosomes reaching the poles while those of the Aegilops parent are 

 still in metaphase. 



In addition to the irregular meiotic division, abnormalities occur in 

 the formation of the pollen tetrads, which result in the production of 

 multinucleate pollen grains, containing from 2 to 4 nuclei of very variable 

 size and chromosome constitution. 



(ii.) (Aegilops ovata t > Triticum vulgare c)^ Triticum vulgare *, - 

 Aegilops triticoides 9 * Triticum vulgare - Aegilops speltaeformis, 

 Jordan. - A fierce controversy arose among botanists regarding Aegihps 

 triticoides and its transformation into ordinary wheat, the polemic being 

 most actively maintained for several years by Jordan and (jodron. 



Jordan with his metaphysical and inflexible views on the immutability 

 of species at first disbelieved the facts described by Fabre, (iodron. and 

 others. He was, however, ultimately constrained to admit that A. triti- 

 coides is a sterile sport or " deformation [of A. ovata] due to hybridisation." 



