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THE AMERICAN NATURALIST [Vol.L 



still is that we are unable to say for eertain whether doubles in- 

 variably occur when the above-named species are crossed 

 with the pollen of a double. When this evidence is available we 

 may expect it to throw further light on the question as to which 

 character is dominant. At present decisive proof on this point is 

 lacking. Comparison with the other types carries us no further. 

 Singleness has been found to be recessive in carnation, hollyhock 

 ;tnd conopsis cambrica; on the other hand, — it is dominant in 

 wallflower and probably in sweet william. 13 Moreover, these 

 forms differ from Petunia in that they give a uniform ¥ t when 

 single and double are mated together. The case of Petunia 

 therefore still remains one of balance of probabilities. In regard 

 to Frost's further suggestion that the facts observed are due to 

 selective sterility I think that this hypothesis may very possibly 

 be correct and certainly has some evidence in its favor. P. 

 vidacea is recognized as a self-sterile species and many of the 

 singles which I used proved to be so. A large number of individ- 

 uals were tested for this character, but further investigation was 

 postponed in the hope of obtaining pure material for comparison. 

 If Frost's hypothesis is confirmed for Petunia, and the work of 

 Belling 14 and East 15 points in this direction, it may offer a com- 

 plete explanation of the facts and render the supposition of a 

 differential distribution of factors to ovules and pollen in this 

 genus unnecessary. 



Edith K. Saunders 



GAMETOGENESIS IN PLANTS 

 The evolutionary origin of the reproductive cells furnishes 

 one of the most fundamental problems connected with genetics, 

 for upon a clear understanding of the subject depends the satis- 

 factory solution of many subsidiary problems relating to animal 

 and plant breeding. The value of hybridization and inbreeding ; 

 the meaning of the pure line hypothesis ; the principle of cumu- 

 lability, etc., may here be mentioned. Therefore, whether or not 

 one agrees with the conclusions presented, studies from widely 

 13 Saunders (unpublished) . The carnation has also been investigated by 

 Norton. (See paper read at the meeting of the Society of Horticulture in 

 Philadelphia in December, 1904. Also Gard. Chron., Jan., 1905.) 



