210 GENETICS AND EUGENICS 



served the occurrence of similar genetic changes in Arcella. 

 It is evident that on the theory that genes are the exclusive 

 vehicles of inheritance, it must be supposed that genes are 

 undergoing change rather frequently in the asexual repro- 

 duction of Difflugia and Arcella. 



In the asexual reproduction of plants genetic changes 

 known as bud-variations occasionally occur. East (1910) 

 has observed, in the reproduction of the potato by tubers, 

 changes in the shape, color, or depth of eyes of the tubers, 

 such as are known to behave as simple unit-character varia- 

 tions in reproduction by seed. It seems probable therefore 

 that they have arisen as changes in single genes occurring in 

 asexual reproduction. In the propagation by budding of 

 citrous fruits and of prunes, according to Shamel, genetic 

 changes of commercial importance occur with so great fre- 

 quency that it seems desirable to take budding stock only 

 from carefully selected trees within the variety. The varia- 

 tions noted affect especially the shape and size of the fruit, 

 or the vigor and productiveness of the tree. Shamel de- 

 scribes thus the recent origin of a new and improved variety 

 of the French prune. (See Fig. 133.) 



In 1904, in a French prune tree growing in an orchard near Saratoga, 

 Cat, one branch high up in the tree was found bearing very large fruits. 

 There is no question as to its being a true bud variation. Several grafts 

 were secured from this branch and placed in bearing peach trees in order 

 to secure early evidence as to whether this variation, or bud sport, could 

 be propagated. The fruits produced by these grafts were found to be iden- 

 tical to those borne by the original branch. The large fruits possessed all 

 of the desirable characteristics of the smaller fruits of the ordinary French 

 prune and, in addition, possessed the desired improvement in size. 



In order to give this strain a commerical test Mr. Coates bought 10 

 acres containing about 1000 peach trees for experimental trials of the 

 large prune variety. These trees were five years old in 1914 at the time 

 of their purchase. The large-fruited French prune variety was budded 

 into every other row of the peach trees with the usual method practiced 

 in top-working citrus and other fruit trees. 



The top-worked trees with the improved French prime strain, called 

 No. 1418 for convenience during the experimental stages, are in alternate 

 rows with the ordinary or other selected strains of the parent variety. 

 In other words, in the 10-acre experimental orchard there is one row of 

 No. 1418 followed by a row of the parent variety, and so on throughout 



