KNOWLEDGE OF HEREDITY IN PISUM. 109 



ter upon an embryo which is incapable of transmitting any 

 trace of the character in question. Some of the dimpled seeds 

 upon a heterozygote plant derived from the cross between 

 dimpled and round give rise to plants in which no trace of 

 the dimpled character is to be observed. 



These phenomena lead to a remark upon the one possible 

 source of confusion for inexperienced experimenters with 

 seed characters, wliich lies in the fact that the testa of a seed 

 Oil the one hand and on the other the embryo, including the 

 cotyledons, belong to distinct generations. As compared 

 with the cotyledons, the testa is a maternal tissue. When 

 segregation is going on, therefore, it is the rule for all the 

 testas upon the same plant to be alike, but the cotyledons of 

 the different seeds of one plant may be different. To this 

 rule the above cases constitute notable exceptions. 



Postscript. 



In " Nature " for August 22, 1907, there appears an anony- 

 mous statement to the effect that no one has repeated Mendel's 

 experiments with the deliberate intention of testing the 

 Mendelian interpretation of the results. The curiosity natur- 

 ally excited by this statement as to what other object — in the 

 opinion of the writer of the review — could have been in the 

 minds of all those who have laboriously continued Mendel's 

 inquiries, is only partly allayed by the explanation of the same 

 writer in ' ' Nature " of September 12. Here we find that what 

 was meant was that crucial experiments had not been carried 

 out by sceptical* observers on certain lines which are indicated. 



In addition to numerous crosses between heterozygote and 

 recessive carried out with sufficiently conclusive results in 

 the case of peas, the present writer has actually carried out 

 on a considerable scale an experiment with Zea Mays on lines 

 closely similar to those indicated in ' 'Nature " of September 12, 

 1907. An account of these experiments appeared in ' ' Nature " 

 of October 20, 1904, and a full description of them has since 

 been published (27). 



* My italics. — R. H. L. 

 7(6)08 (14) 



