174 PLANT-BREEDING 



recommended for millinery purposes and may supplant a 

 large part of the trade in artificial flowers. I admired, on 

 each of my three visits, the large beds full of the shiny red 

 flowers, and saw the selection of the largest and brightest 

 specimens going on. 



The main work of Burbank, however, consists in pro- 

 ducing new varieties by crossing. The aim of crossing is 

 the combination of the desirable qualities of two or more 

 species and varieties into one strain, and the elimination of 

 the undesirable characters. In the most simple cases this 

 can be produced by one cross and without selection; but, 

 ordinarily, many crosses and the production of a more or 

 less chaotic progeny are required, and selection has to decide 

 what is to live and what is to be rejected. It is a well known 

 fact, discovered by Koelreuter and Gartner and confirmed 

 by numerous other scientific hybridologists, that hybrids 

 often surpass both their parents in the vigor of their growth 

 and the profuseness of their flowering. Taking advantage 

 of this rule, in more than one instance Burbank has pro- 

 duced hybrids of extreme capacities. The most astonishing 

 instances are afforded by his hybrid walnuts. In the year 

 1891, he crossed the English walnut and the Calif ornian 

 black walnut and afterward planted a row of them along the 

 road before his residence. At the time of my first visit, six 

 gigantic trees were seen growing. They had reached twice 

 the height and size of ordinary walnut trees. Three of 

 them he has since been compelled to cut down, because they 

 increased too rapidly. This summer (1906) I saw the three 

 remaining specimens, 80 feet in height and 2 feet in diameter. 

 He showed me sections of the cut stems. Their wood was 

 of a fine grain, very compact and of silky appearance. The 

 annual layers measured about 5 cm., a most extraordinary 

 thickness. Fast growing trees are usually of soft grain, but 

 these hybrid walnuts have a wood as hard as that of the 



