SHOBTER ARTICLES AND DISCUSSION 



ANOTHER HYPOTHESIS TO ACCOUNT FOR DR. 

 SWINGLE'S EXPERIMENTS WITH CITRUS 



The results of the cross-breeding experiments with forms of 

 Citrus by Walter Swingle have given rise to quite a number of 

 different hypotheses, to account for the facts observed. 



The facts are simply these. All the different forms of Citrus 

 used in the experiments. Citrus trifoliata. the lemon, orange and 

 other citrous fruits have, so far, proved to reproduce their own 

 type through seed. 



Nevertheless, the plants raised from one single cross are ex- 

 ceedingly different among themselves. And yet, all these new 

 forms, for so far as tested, have proved truly to reproduce their 

 own kind only, if sown. 



The theories offered to account for these facts are rather com- 

 plex. So far, we have not seen the simple hypothesis which we 

 want to add to the others. 



The fact, that the F x from almost every cross between types of 

 Citrus is multiform, can only be accounted for on the assumption, 

 that the parent plants are impure (heterozygous) for a number 



for a number of genes, produce seed which always only repro- 

 duces the type? We know, that if a plant reproduces itself 

 by an asexual method, all its daughter plants are pure for 

 those genes in respect to which it was pure, impure for those 

 genes for which it was impure. Is it possible that in these 

 trees the seeds normally produced are not derived from a union 

 between two normal gametes ? In Citrus, with its adventitious 

 embryos, this is very well possible. If the forms of Citrus used 

 by Dr. Swingle are self-sterile, the seeds normally produced by 

 these trees, are not produced by the union of two gametes, but 

 as buds, asexually. 



This hypothesis, that the Citrus used are self-sterile, and that 

 the seeds normally produced, are produced asexually, fully ac- 

 counts for all the facts. All the daughter plants from Un- 

 as in all clones. On poll-m/at mn by another tree, normal seeds 



