256 Earhj and Late Ripenhuj in an Oat Cross 



The general conclusion arrived at as the result of this experiment 

 therefore is that there is ground for supposing that early and late 

 ripening are mendelian characters, but that they are dependent on 

 more than one factor, possibly three. F., })lants homozygous for one of 

 these, it would seem, are definitely early in the sense that their F.^ 

 rows all reach complete ripeness before any individuals of the late 

 parent are mature ; yet, in all except 2 cases out of 24, they cannot be 

 called exactly as early as Mesdag. Apparently it required homozy- 

 gosis in all three factors to produce these two perfectly early rows. 

 The diversity of the remaining 22 early ripeners, where in some 

 cases (e.g. Nos. 20, 52) the accumulation of the ripening occurs 

 during the first part, in others (e.g. Nos. 28, 44, 54, 61, 72) in the 

 middle, in others again (e.g. Nos. 29, 49, 71) at the end of the period 

 from Aug 10th to Sept. 4th, certainly supports the inference that 

 although one factor is here constant and homozygous, thus imparting a 

 common measuie of earliness, the other two, in various heterozygous 

 and homozygous combinations, are responsible for the ditlerent in- 

 cidences of the greatest intensity of this earliness. 



There can be little doubt, too, that the extent of the tillering has 

 much to do with the rate of ripening. The tillering power of late 

 forms is always good ; that of early, very poor. Owing to the con- 

 centration of growth among early plants into one or two panicles only, 

 these are generally bigger and bear better grain than those of late 

 plants ; but this advantage does not compensate for the diminished 

 yield due to the small number of heads. There is thus an inevitable 

 sacrifice of crop when it is attempted to render a late kind early. The 

 only hope, apparently, lies in increasing the output, per individual panicle, 

 of an already early variety. This can best be done by extracting it again 

 from a fair-sized F.^ generation of a cross with a type which, quite apart 

 from any ability to tiller profusely, has above all larger panicles and 

 larger grain of better cpiality. 



Summary. 



1. Earliness and lateness are not instantaneous, sharply defined 

 characters : they are spread over a period. 



2. The ripening times of the parents used did not overlap. 



3. Poor tillering })ower was characteristic of the early parent. 



4. F^ plants more or less intermediate. 



