362 Doubleness in Stocks 



The present series of experiments has made it abundantly clear that 

 singleness or doubleness in the flower is a character which is dependent 

 solely upon the constitution of the germ cells from which it arose ; that 

 it is in fact already determined in the seed, and is entirely independent 

 of external conditions. Though the present results have disproved the 

 interpretation, they have confirmed the fact observed by Thiele, Cliate 

 and others that the proportion of doubles obtained from old seed is 

 often higher than that given by seed mure recently harvested. They 

 have also furnished incidentally a certain amount of evidence as to 

 the relative viability of the seeds giving rise to singles and doubles 

 respectively, and also as to the possibility of identifying those which 

 give doubles. 



(a) Viability. 



Although critical experiments on a very large scale, and specially 

 designed to this end, would be required to show the relative rates at 

 which the progressive loss in germinating power occurs among seeds 

 destined to give rise to singles and doubles respectively, the evidence 

 already available points strongly to the conclusion that in any lot of 

 seed which has been kept until the bulk of it is no longer capable of 

 germination the surviving remnant will be mostly if not exclusively 

 composed of those yielding doubles'. The effect of this greater viability 



' It ia perhaps hardly necessary to state that the tirae during which the seeds retain 

 their vitality varies greatly with the quality of the seed. Cent, per cent, germinatiou 

 was obtained in some cases after the lapse of three years ; even after seven years — the 

 longest period over which sample sowings from any one lot of seed were extended — a few 

 still retained their vitality. On the other hand badly ripened seed sometimes failed 

 altogether to germinate after three, or even two years. 



In considering the results of repeated sowings made after a considerable lapse of time 

 the following point must be borne in mind. Where only a small number of seedhngs 

 are obtained, it may be that all or most of the seeds in one or two better ripened pods 

 have retained their vitality while those belonging to all the other pods have died ; or on 

 the other hand it may be that only a seed here and there in each of several pods has 

 survived. In the former case the original ratio of single to double will presumably 

 be unchanged ; only in the latter case are we concerned with the question of a differential 

 death-rate. Unless the seed is unmistakeably of uniform quahty, it is therefore desirable, 

 in experiments designed to test this point, that the seed of individual fruits should be 

 sown separately, though this method of procedure necessarily entails much waste of 

 space when very few of the seeds still survive. When the further fact is taken into 

 account that single fruits are often found not to afford average samples it will be seen 

 that any comparative experiment will be of little value unless carried out on a very 

 considerable scale. Furthermore only those cases should be taken into account in which 

 all or most of the remnant which germinated survived to flower. Where the number of 

 plants involved is in any case very small, the loss of several individuals before the 

 Uowering stage may render the result quite untrustworthy. 



