10 , Messrs. P. de Vilmorin and W. Bateson. [Mar. 2, 



As the case was almost certainly one of gametic coupling between 

 roundness of seed, and tendrils, the problem was clearly worth minute 

 investigation, and a quantity of material was transferred to the John Innes 

 Horticultural Institution, Merton, Surrey, for this purpose. The offspring of 

 two F 2 plants, heterozygous in both respects, were, in particular, the subject 

 of study. 



Unfortunately, the distinction between rounds and wrinkleds was in these 

 families not perfectly sharp, and much irregular pitting occurred. When the 

 plants grown from these seeds were harvested it was found that errors in 

 sorting had been made both ways, one seed having been sown for a round 

 which gave rise to a plant with exclusively wrinkled seeds, and two seeds 

 which had been sown as wrinkled proved to have been heterozygous rounds. 

 The earlier counts had therefore to be rejected, and in order to obtain 

 perfectly reliable numbers it was clearly necessary that the nature of the 

 starch in each seed should be separately determined for each seed before it 

 was sown. As Gregory* had observed, by microscopical examination of the 

 starch grains, this discrimination may be made without difficulty. 



The microscopical test was applied by Miss C. Pellew, Minor Student of 

 the Institution, to F 4 seeds of heterozygous plants on a considerable scale, 

 and the seeds were then sown. Only a fragment of a cotyledon need be 

 removed for testing, and the seeds germinated perfectly after the operation. 

 The results were as follows : — 





Round. 



Wrinkled. 



Tendrilled. 



Acacia. 



Tendrilled. J Acacia. 





319 



333 



4 



3-4 



3 123 



3 -4 1 109 



Calculated on a coupling of 63 : 1 ... 



These figures leave no reasonable doubt that the system of gametic 

 coupling followed in this case is 



63 TK : 1 Tr : 1 tE : 63 tr, 

 where T is tendrilled, and E is round seed. This gametic system gives the 

 zygotic ratio 



12161 TE : 127 Tr : 127 tE : 3969 tr = 16384, 



from which the above calculation is made. This particular system has not 

 been hitherto encountered, but it is, of course, one of those contemplated by 

 the general expression for coupled systems. 



* ' New Phytologist,' 1903, vol. 2, p. 226. 



