THE HISTORICAL DEVELOPMENT OF BIOLOGY 545 



Law III. Hybrid bred with hybrid, xy plus xy makes xx, -\-2xy, 

 +yy or stated differently. 



xy . . xy x y hybrid 



t\ >"' 



i 



*" y. hybrid 



xx xy_ yx_ yy xx xy 



2 xy yx yy 



xx 2xy yy 



Luther Burbank. No one has made such successful applica- 

 tion of these laws of inheritance as has Luther Burbank. For 

 years he has been performing what might be called biologic miracles, 

 on his farm in Southern California. 



A complete list of the new or improved plants which he has de- 

 veloped, would occupy a whole chapter, but some of the most 

 famous are 



1. The Burbank potato which has increased our crop by mil- 

 lions of dollars and is said to have prevented the potato famine 

 that formerly devastated Ireland. 



2. The spineless cactus which provides abundant stock food 

 for regions where none was to be had. 



3. The " Primus Berry," a valuable cross between the dew- 

 berry and raspberry. It differs from both its ancestors and is the 

 first absolutely new species ever produced by man. 



4. A cross between the plum and apricot called the " Plumcot " 

 which has the good qualities of both ancestors and some of its own. 



5. The pitless plum and thin-shelled walnut explain themselves. 



6. Among flowers, the Shasta daisy six inches in diameter, and 

 the ten -inch poppy, are well known. 



He works by cross-pollenation, grafting, and rigid selection. 

 Specimens are collected from all over the world, raised in his 

 gardens, and crossed to develop desirable characteristics. They 

 are then cultivated in enormous numbers, to take advantage of all 

 possible variations, and only the best are selected. 



Thus, by combining a deep knowledge of biologic laws, with 



