Principles of Heredity 141 



Giltay states, has a transparent skin, and the only xenia 

 likely to occur in the other cases would be of the peculiar 

 and uncertain kind seen in using "grey" peas. Professor 

 Weldon notes that Giltay, who evidently worked with ex- 

 treme care, peeled his seeds before describing them, a course 

 which Professor Weldon, not recognizing the distinction 

 between the varieties with opaque and transparent coats, 

 himself wisely recommends. The coincidence of the peeled 

 seeds giving simple Mendelia.ii results is one which might 

 have alarmed a critic less intrepid than Professor Weldon. 



Bearing in mind, then, that the coats of peas may be 

 transparent or opaque ; and in the latter case may be 

 variously pigmented, green, grey, reddish, purplish, etc. ; 

 that in any of the latter cases there may or may not be 

 xenia ; the reader will perceive that to use the statements 

 of an author, whether scientific or lay, to the effect that on 

 crossing varieties he obtained peas of such and such colours 

 without specifying at all whether the coats were transparent 

 or whether the colours he saw were coat- or cotyledon-colours 

 is a proceeding fraught with peculiar and special risks. 



(1) Gartner s cases. Professor Weldon gives, as ex- 

 ceptions, a series of Gartner's observations. Using several 

 varieties, amongst them Pisum sativum macrospermum, 

 a "grey' : pea, with coloured flowers and seed-coats*, 

 he obtained results partly Mendelian and partly, as 

 now alleged, contradictory. The latter consist of seeds 

 "dirty yellow " and "yellowish green," whereas it is 

 suggested they should have been simply yellow. 



Now students of this department of natural history will 

 know that these same observations of Gartner's, whether 

 rightly or wrongly, have been doing duty for more than 

 half a century as stock illustrations of xenia. In this 



* Usually correlated characters, as Mendel knew. 



