314 Doiibleness m Stocks 



accidental and unimportant : or, if we had grounds for supposing that 

 we were dealing with a race in which some, but not all, of the pollen 

 grains were carrying doubleness. But neither supposition agrees well 

 with the facts. The evidence from cross-breeding, so far as it goes, 

 indicates that here, as in the sap-coloured forms, all the pollen grains 

 carry the double character; for, as shown in Table I, 20 Fi plants 

 derived from the mating no-d-creara $ x c^-white </• were tested, the 

 pollen grains from which they were derived having been furnished half 

 by plant B and half by plant / ; all yielded doubles when self-fertilised. 

 On the other hand the fact that results precisely similar to those 

 described above were obtained with the cream race renders explanation 

 on the accident theory very improbable. 



ii. Glabrous cream race. 



Seeds of the cream race were obtained from the same sources as 

 those of the white, and here too, in accordance with expectation, doubles 

 occurred in both sample sowings (see Table II). 



In the case of lot 1 only three of the singles were tested, one (A) by 

 self-fertilisation, the other two (B and X) by cross-breeding. All three 

 yielded doubles, either in Fi (as a result of self-fertilisation or of crossing 

 with a d-strain) or in F^ (when the mating was with a no-d-strain), as 

 did also the two descendants of the self-fertilised plant A which were 

 tested (viz. plants iV^ and 0). In addition to these 5 plants, 12 singles 

 derived by cross-breeding from B were also tested ; each yielded doubles 

 in the next generation, a result which further confirms the eversporting 

 character of plant B. 



In the case of lot 2, where more individuals were bred from, the 

 results indicate on the other hand that, as was found with the white 

 race, the singles were mixed, some yielding doubles and some not. Out 

 of 11 singles taken at random from this batch 10 were tested by self-, 

 1 by cross-fertilisation ; of these, 4; (plants C, D, E, F) appeared to be 

 breeding trueS the remaining 7 (plants G, H, /, J, K, L, M) produced 

 doubles either in the next generation, or in F2 if the mating was with 

 a no-c^-strain as was the case with plant M. In the case of plants 

 G and H the ofifspring were too few to give indication of the true 



1 The number of offspring obtained from plant F by self-fertilisation was only 3 — far 

 too small a total to be taken as proof that the absence of doubles is real, but the evidence 

 from cross-breeding leaves no doubt that F was a pure-breeding single. Used as the 

 S parent in a mating with no-d-white it produced 10 plants in Fi, 9 of which were self- 

 fertilised, yielding altogether a total of 70 plants in F^ which were all single. Further, 

 when used as ? with two rf-strains the 23 individuals obtained in Fi were all single. 



