W. Neilson Jones and M. Ciikvklv Kaynek -205 



(c) That there is nei'd tor caution by systeinatists in distingui.shing 

 new species, especially in the case of large geneia, e.g. Rasd, Rabiis, 

 etc., in which there is a tendency fco iinilti})ly number of species to an 

 inordinate extent. 



It appears likely from an analysis of the results obtained from 

 crossing two such forms in Bryony, that many of these so-called 

 "species" are natural hybrids which occur as segregates from inter- 

 crossing among a comparatively small immlnTof forms which breed true 

 to type. 



The genctical behaviour of the differentiating characters cited 

 above will now be considered. 



A. Blouin on the hernj (.5). 



The ripe berries of the two varieties B and G differ in that the 

 berry of G is scarlet with a shining surface, while tluit of /.' is dull 

 crimson in colour with a heavy waxy " bloom." 



The difference in colour is due to a superficial deposit of wax 

 which can be removed by washing in alcohol. 



The essential external difference between the berries is, therefore, 

 the 'presence of " bloom " in variety B and its absence in variety G. 



Genetical behaviuar. 



The hypothesis which satisfies the facts most simply is that absence 

 of bloom (or shininess S) is an almost complete dominant over presence 

 of bloom (.s); presence and absence of bloom depending on the behaviour 

 of a single factor. 



Thus in the cross : 



ss (B plant) x SS(G plant) - (or the reciprocal cro.ss) 



I 

 Fi would give theoretically sS, all without bloom. 



In agreement with this expectation neither of the two female 

 plants obtained fi-om this cross had berries with " bloom." 



In F., expectation gives the following : 

 (a) SS{G)x Ss{t\) 



I ■ 1 



I I 



ISS : l.S's 



all without bloom 



