72 Practical Examples [ch. 



instance, Sutton's " Nonpareil," one of the marrow peas, 

 consists in about equal numbers of yellow-cotyledon seeds 

 and green-cotyledon seeds. Like all the new peas it must 

 have arisen at some definite moment bv the selection of 

 an individual yellow-seeded plant which was true for the 

 various good qualities of Nonpareil — being homozygous for 

 them in other words — but in cotyledon-colour it was 

 heterozygous. As the diversity of colour was not thought 

 objectionable it persists. If any one wishes to make an 

 exclusively green-seeded Nonpareil, all he has to do is to 

 take green seeds from a sack of that variety and sow them, 

 saving the seeds they bear. If he desires the yellow type 

 pure, he may similarly sow yellow seeds from the same sack. 

 Most of these by now will presumably be pure to yellow, 

 but some may not. By keeping the seeds of any plant 

 which gives only yellow seeds a pure yellow Nonpareil will 

 be constituted. 



Similarly Sutton's ** Continuity " is a pea which is 

 allowed to be either pointed in pod or blunt. The variety 

 is true in other respects and it is clear that its original 

 progenitor was a plant homozygous for the peculiarities of 

 Continuity but heterozygous in respect of the pod-shape. 

 The pointed-pod plants would be found true for that 

 character, since it is recessive, while the blunt-pod plants 

 might or might not be true for it. 



So in the Chinese Primrose, several varieties, e.g. 

 Sutton's Mont Blanc, Sirdar, &c., distinguished by peculi- 

 arities of colour have been fixed both in a palm-leaved and 

 in a fern-leaved form, these having of course been saved 

 in F^ or later generations from a heterozygote in which the 

 palm and fern-leaved characters were combined. In Sweet 

 Peas, after the original dwarf " Cupid " was found — accord- 

 ing to tradition a chance seedling among tall plants — it was 

 easy to transfer the characteristic colour of the various tall 

 types on to a Cupid foundation, and now any colour almost 

 can be had either as a tall or as a Cupid. 



Possible Limits to Re -combination. 



These illustrations might be extended indefinitely. It 

 will probably occur to many that there are limits to these 

 possibilities of transference, and so undoubtedly there are. 



