152 Inheritance in the Stock (Matthiola incana) 



hair on the petiole margin of some of the larger leaves. (See later 

 p. 157 where the sub-glabrous forms are described in detail.) So far 

 the partially hoary forms have not been obtained in combination with 

 the full sap-colours. It would seem that either the factors which 

 bring about a diminution in depth of colour and degree of hairiness 

 must be closely coupled, or the same factors must be concerned in 

 producing the dilution effect in both cases. Beyond this fact however 

 we have at present no knowledge of the nature of the bond linking 

 together sap-colour and surface character, and further consideration of 

 this point must be left to the future. 



A further important result of the crossbreeding work is the appear- 

 ance of yet another new grade occupying a position in the series 

 between the half-hoary and the quarter-hoary forms, and hence con- 

 veniently termed the mid-hoary grade. Like the quarter-hoary the 

 mid-hoary form is always heterozygous in constitution. These two 

 crossbreds complete the bridging of the gap, already partly filled by 

 semi-incana, between the condition of maximum effect seen in the fully 

 hoary individual and the stages leading to the complete disappearance 

 of the hairs in the lowest (= absolutely glabrous) grade. In these last 

 stages preceding final disappearance (i.e. in the sub-glabrous grades) the 

 very slight degree of hairiness developed owing to the presence of one 

 only of the two factors causing hair-production is manifested in localised 

 regions of the plant, differing according to which member of the pair 

 is present. Hence it is possible, even in these lower grades, by close 

 inspection, to obtain some information as to their factorial composition, 

 and to dispense with breeding tests. 



It is thus apparent that the two familiar garden types — the fully 

 hoary and the wallflower-leaved — are by no means such isolated forms as 

 they have hitherto appeared to be, but represent the end terms in a 

 graded series, each member of which has a distinct appearance and 

 behaviour corresponding to its factorial composition. As to the order 

 in which the varieties glabra and semi-incana appeared the historical 

 records make no definite pronouncement. Reference to the smooth 

 form can be traced indeed almost as far back as the earliest record 

 known to us of the double-flowered plant (probably 1568)\ Both are 

 mentioned by Parkinson in 1629. In an introductory chapter of the 

 Paradisus terrestris on " the Ordering of the Pleasure Garden " he writes 

 " Stock-Gilloflowers likewise are almost as common as Wall-flowers, 

 especially the single kindes in every womans Garden, but the double 



1 See Dodoens, Florum et coronariaruni 



