368 Douhleness in Stocks 



Note 2. On the inheritance of the branched and 

 the unbranched habit. 



Most races of Stocks branch freely, and in the case of biennial types 

 form large bushy plants. Of the various sorts used in the present 

 experiments the Ten Week strains all have the branched habit, as have 

 also among the biennials, incana and the Brompton strains raised by 

 Continental growers. The typical English Brompton is on the other 

 hand wwbranched, the single stout stem being prolonged above the 

 region of the leaves as a simple raceme. Both leaves and fruits in this 

 type are thick and somewhat fleshy. The unbranched habit is recessive 

 to the branched. "When a cross is made between an English type of 

 Brompton and a branched form the Fi cross-breds are bushy plants like 

 incana. In F^ the pure Brompton habit reappears in a proportion of 

 the plants. The sorting of the F^ plants is rendered difficult owing to 

 the fact that the formation of branches can no doubt be induced by a 

 variety of causes producing a check in growth. An injury to the 

 terminal bud or to the roots may cause a check in the growth of the 

 main axis and lead to the development of one or more axillary buds 

 which otherwise would have remained dormant. Injuries of this kind, 

 resulting in a check to growth, are very likely to occur when the young 

 plants are planted out, and hence in a strict count a certain number 

 of individuals are likely to be classed as normally producing branches 

 which in fact only do so owing to unfavourable conditions, or to accident ; 

 thus the proportion of individuals inheriting the unbranched habit is 

 likely to appear less than it actually is. In the one mating in which 

 an English Brompton stock was crossed with a branched form 394 plants 

 were raised in F^. Of these 66 were recorded as typical Brompton 

 plants and 31 others as being unbranched except for a single lateral. 

 These numbers suggest that the true proportion of plants inheriting 

 the unbranched habit in F^ is probably 1 in 4 as in the ordinary case 

 of a simple recessive. 



The characteristic appearance of the unbranched as compared with 

 a branched type is shown in the accompanying figures showing two 

 of the Ffi plants derived from a cross between an English Brompton 

 and a branched Ten Week strain. (Fig. 1 shows the branched, fig. 2 the 

 unbranched habit.) The photographs were taken at the end of the 

 season when the plants were in fruit and the leaves had fallen. In the 

 Fi generation the Brompton plants presented a very curious appearance, 

 the single stem in many cases reaching a height of from 3 to 3| feet. 



