SOME EXPERIMENTS OF LUTHER BURBANE. 209 



"In some directions the strains of heredity are much more unbal- 

 anced than in others. An impulse from outside forces may bring about 

 new combinations. This is illustrated by De Yries by a ball with many 

 facets, which, if lightly touched, will return to its original position, 

 if vigorously touched will turn over. Burbank once crossed a pole bean 

 (Phaseolus vulgaris) with a lima bean (Phaseolus lunatus var. macro- 

 carpus). There was no visible effect in the appearance of the pod or 

 the bean, but, when planted, each bean developed a cotyledon, part of 

 one species and part of the other. The lima bean represented the end 

 _ofjthe cotyledon, and was united to the lower part by serrated edges; 

 below was the smaller and striped cotyledon of the pole bean. The 

 cotyledons finally parted at the joints between the two, the upper por- 

 tion falling off, as is often the case with grafts which are uncongenial. 

 The forms were tremendously vigorous, but all came back to the com- 

 mon pole or horticultural bean after the second generation, as though 

 it were an uncongenial graft hybrid, the alien portion being finally 

 •entirely rejected. It often happens in grafting, that the branch will be 

 united thoroughly at the point of grafting, but in great stress,. as the 

 overbearing of fruit, the grafted portion will separate and entirely fall 

 off." 



" In one sense, hybridization is only a mode of grafting, both being 

 a more or less permanent combination. The different results from 

 hybridization are shown in the diagram below." 



" Where the plants are very different, having a different line of 

 descent, and consequently different structure, there will be no hybrid- 

 ization at all. From this we have every gradation to the point where 

 the individuals are very closely alike, and here we have scarcely any 

 variation at all in the progeny, a condition which favors extinction. 

 Again, in grafting, we have every intergradation between total inability 

 to unite and absolutely perfect blend." 



" Sometimes a graft strengthens a plant by increasing the body of 

 foliage and thus strengthening the roots. Grafting a Japanese pear on 

 the Bartlett pear will give the latter new life through the increase in 

 the foliage, which gives material for root action and further extension." 



As illustrations of the results of crossing and hybridization, the 

 following notes were taken on plants in Mr. Burbank's gardens : 



In the beginning of his work Mr. Burbank crossed all sorts of beans 

 and had a half acre of them. Some climbed to the height of twenty 

 or thirty feet, producing all sorts of pods — some with pods long and 

 slender and stems so short that the pods doubled up on the ground. 

 These forms could have been fixed in time, though the variations were 

 unusually persistent and very amazing in their variety and abundance. 



Crossing the red and white pole bean, two or three of the beans 

 grew large and bore striped pods, the beans themselves being jet black. 



