386 GENETICS IN RELATION TO AGRICULTURE 



pagated. Careful inspection may reveal a certain number of chimeras 

 and bud sports. Both, in fact, are comparatively common in some 

 varieties, such as the Boston Fern and the Washington Navel Orange, 

 and they sometimes give rise to superior new biotypes. Yet inspection 

 alone is not sufficient. A new fern sport must be propagated in order to 

 test its constancy when multiplied vegetatively. Similarly a supposed 

 orange sport must be propagated and the progeny must be tested in 

 order to ascertain whether the selected phytomer is really a mutation 

 and a desirable one at that. 



Having discovered a new type which originated by bud mutation, 

 the question arises : Will there be any practical difficulty in maintaining 

 this new form by means of vegetative propagation? Are additional 

 somatic mutations likely to occur in sufficient number to endanger the 

 preservation of the selected form? It will be remembered that sometimes 

 bud mutations in the Boston Fern produce ever-sporting varieties that 

 have little or no commercial value. Similar inconstant forms have 

 arisen in other ornamentals. Nevertheless it has been practicable 

 to propagate vegetatively many valuable bud sports and hybrids, in- 

 cluding some that are highly variable. One such product of composite 

 hybridization is the cultivated Coleus. This ornamental foliage plant 

 is commonly used for beds and borders in summer and as a conserva- 

 tory plant in the colder months. The foundation stock was produced 

 in England about 1867 by hybridizing four different exotic species. 

 Hundreds of named varieties have been produced, some having appeared 

 as bud mutations, but the majority being seedlings. Some of the varie- 

 ties now in cultivation are characteristically variable. In one such 

 variety Stout has investigated the variations in leaf color pattern and 

 leaf shape in a series of 833 plants, all descended by vegetative 

 propagation from two similar plants. 



Bud Selection in Coleus. The two plants with which Stout began 

 had a definite pattern of leaf coloration consisting of a green mid-region 

 and yellow border with blotches of red in the epidermis (Fig. 159). The 

 green and yellow pigments exist in the sub-epidermal layers. The 

 vegetative offspring from the two original plants were kept separate and 

 the simple habit of branching in this plant made it possible to indicate 

 the particular branch as well as the individual plant from which a cutting 

 was taken. In this way Stout was able to trace the pedigree of any plant 

 to its original source. During the course of the investigation 16 new 

 color patterns were obtained. There also appeared the laciniate form 

 of leaf which is seen in the younger leaves of the plant on the left in Fig. 

 159. Of the 16 new color patterns 15 arose by somatic mutations which 

 produced bud sports either directly or, in some cases, indirectly from 

 chimeras. The other new pattern arose solely as a fluctuating variation. 



