206 PLANT-BREEDING 



the most famous among the older species of garden flowers 

 and their hybridizations, as for example the Begonia, the 

 Amaryllis, the Gladiolus, and many others, we find that 

 progress has, in the main, been slow, advancing only by 

 more or less accidental leaps. These advances were the 

 result of the discovery or introduction of new promising 

 species and of their being worked into the strain. They 

 often mark distinct periods in the progress of these hybrid 

 families, and not rarely they have been achieved by different 

 breeders. In such cases, the history of the whole strain 

 may be more or less easily traced. Opposed to these suc- 

 cessive introductions of new species into a hybrid family, 

 is Burbank's principle to start at the very outset with as 

 many promising species as possible, in fact with all that may 

 be available in any nursery or botanical garden, or may be 

 collected in their native haunts in any part of the world. 

 The Callas give a beautiful instance of this method, five 

 new types having been added at once to the original stock. 

 Of course, each of them has brought its peculiar character 

 of flowers, foliage, and mode of growth, and an almost endless 

 range of combinations must be the result. Calla hastata is 

 a yellow species from the Congo; Elliottiana is of a still 

 richer and darker yellow and has spotted leaves; Pentlandi 

 is yellow with a dark purple spot; Rehmanni is pink on 

 the outside and rose purple with a crimson spot within; 

 Nelsoni is small, pale yellow and purple. All these new 

 types have been variously crossed among themselves and 

 with the old white kinds. Of course, the crosses were made 

 partly with definite combinations in view, and partly as 

 occasions were offered, and the seeds of the crosses were 

 saved and sown in mixtures. Each single hybrid of the next 

 \ generation manifestly had only two parents and thus a second 

 and even a third season of crossing were required to obtain 

 combinations of a higher rank. Thus the range of varia- 



