W. Neilson Jones and M. Chevely Rayner 219 



decide with certainty from iippearances only whether another plant is 

 one of the more extreme forms of G or a G-like type of hybrid. Only 

 breeding tests could decide this satisfactorily. 



It would seem therefore that, nn crossing plants with the Ji and G 

 types of foliage respectively, segregation occurs in the second genera- 

 tion resulting in the re-appearance of the original types and also of 

 many intermediate hybrid forms — the range of variation in any typo 

 being such that overlapping occurs with those adjacent to it. 



Independent observations during successive years indicate that the 

 leaf-type of individual plants remains sensibly constant within a small 

 range of variation, and that if it were possible to express the results 

 more precisely, the different hybrid-types might be definitely recognized 

 and distinguished. 



Similar observations apply to the other vegetative characters men- 

 tioned, such as colour and texture of leaves, and degree of hairiness : 

 plants showing the characters of the grandparents appear in the F.. 

 generation, together with a number of intermediate forms difticult to 

 classify precisely. 



Since several pure G and pure B plants occur in the family of 38 

 from the cross F^ x F^, the factors determining leaf-shape are probably 

 few in number, but no attempt has at present been made to analyse 

 the ultimate anatomical characters which determine the shape, colour 

 and texture of the leaves. 



Records were made of the length of internodes on shoots of plants 

 of both varieties and of their hybrids, but, up to the present, a simple 

 method of presenting such records has not been devised. 



It seems not improbable that the differences in length of internode, 

 shape and texture of leaves, and number of vascular bundles in the 

 stem internode may be closely correlated and connote a difference of 

 phyllotaxy in the shoots of the two vai'ieties. This point is not readily 

 determined by external observations in a climbing plant and awaits an 

 independent investigation. 



Although the numbers of plants employed in these experiments 

 were not sufficient to yield trustworthy ratio-numbers, the facts are 

 believed to be of interest inasmuch as they point clearly to Mendelian 

 inheritance of characters distinguishing plant forms of " sub-specific " 

 rank ; and following from this, they emphasize the pressing need for 

 revision of systematic nomenclature when new species are separated 

 on morphological characters alone, without reference to genetical 

 behaviour. 



