Principles of Heredity 131 



Of course there may be exceptions. As yet we cannot 

 detect the causes which control them, though injury, 

 impurity, accidental crossing, mistakes of various kinds, 

 account for many. Mendel himself says, for instance, that 

 unhealthy or badly grown plants give uncertain results. 

 Nevertheless there seems to be a true residuum of ex- 

 ceptions not to be explained away. I will recite some 

 that I have seen. In my own crosses I have seen green x 

 green give yellow four times. This I incline to attribute 

 to conditions or other disturbance, for the natural pods of 

 these plants gave several yellows. At Messrs Suttons' I saw 

 second-generation seeds got by allowing a cross of Suttotis 

 Centenary (gr. wr.) x Eclipse (gr. rd.) to go to seed ; the 

 resulting seeds were both green and yellow, wrinkled and 

 round. But in looking at a sample of Eclipse I found 

 a few yellow seeds, say two per cent., which may perhaps 

 be the explanation. Green wrinkled x green round may 

 give all wrinkled, and again wrinkled x wrinkled may give 

 round*. Of this I saw a clear case supposing no mistake 

 to have occurred at Messrs Suttons'. Lastly we have 

 the fact that in exceptional cases crossing two forms 

 apparently pure in the strict sense may give a mixture 

 in the first generation. There are doubtless examples also 

 of unlikeness between reciprocals, and of this too I have 

 seen one putative caset. 



Such facts thus set out for the first cross-bred 

 generation may without doubt be predicated for subsequent 

 generations. 



What then is the significance of the facts ? 



* Professor Weldon may take this as a famous blow for Mendel, 

 till he realizes what is meant by Mendel's " Hybrid-character." 



f In addition to those spoken of later, where the great difference 

 between reciprocals is due to the maternal characters of the seeds. 



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