48 



The Journal of Heredity 



ten plants that were simple-leaf 

 throughout. 



Four thick-leaf sports have been ob- 

 served by the writer in four different 

 Maine fields, three in the Green Moun- 

 tain variety and one in the Ehnola 

 variety. Only one will be described 

 here. It originated in a Green Moun- 

 tain hill-selection strain grown and ob- 

 served for foliage diseases from 191 5 

 to 1920, inclusive. This hill-selection 

 strain produced only one thick-leaf 

 sport, as one hill in a total of 158 

 grown in 191 8. The original thick- 

 leaf hill had two branches almost nor- 

 mal and two branches with distorted, 

 thxk or fleshy, glabrous leaflets. Of 

 the second, third, fourth and fifth gen- 

 erations, grown in the field the next 

 four summers, each showed a range 

 from absence to completeness of sport- 

 ing among the various hills, and even 

 among the various leaves of one hill, 

 and among the leaflets of a single leaf. 

 Fig. 19 shows a completely abnormal 

 leaf and one partly normal. The orig- 

 inal plant in 1918 yielded six tubers, 

 which in 191 9 produced sixteen plants 

 of which nine were more or less ab- 

 normal. Seven of these nine hills were 

 kept. The percentage of their leaf 

 area estimated to be abnormal, ranging 

 from ten to one hundred per cent for 



the different plants, was not correlated 

 with the abnormality percentages of 

 their progeny hill-lots. In 1920. ten 

 hills were selected as having less than 

 half of the foliage abnormal, and ten 

 with more than half. These two ten- 

 hill parts of the strain were not ob- 

 viously different from each other in 

 1921, though as previously stated, there 

 was a complete range of difference be- 

 tween hills. Only a few of the most 

 abnormal hills were kept in 1921, but 

 in 1922 there was again a variation, 

 normal or partly normal foliage ap- 

 ]iearing. It seems, then, that the thick- 

 leaf type of sport, though probably oc- 

 curring more frequently than the 

 simole-leaf type, is somewhat less 

 stable. 



Partial recovery after two genera- 

 tions of complete abnormality, with 

 normal leaflets or leaves then appearing 

 with abnormal ones as parts of the 

 same structure, precludes these sports 

 from being classed with degeneration 

 diseases. From such diseases there is 

 no true recovery as long as propaga- 

 tion is by tubers,^ and apparent re- 

 covery (climatic suppression of symp- 

 toms) is not confined to indiscrimi- 

 nately scattered leaflets, leaves, and 

 plants. 



Literature Cited 



^FoLSOM, Donald. Potato Mosaic. Maine Agric. Exp. Sfa. Bui 232:157-184. Fig. 

 28-30. 1920. Potato Leaf roll. Maine Agric. Exp. Sta. Bui. 297:37-52. Fig. 29-35. 1921. 



" HrxcERFouiJ, Chas. W. Leafroll, Mosaic and Certain Other Related Diseases in Idaho. 

 Phytopathology, 12:133-139. PI. ix. 1922. 



■■' MacKelvie, Donald. "Bud Variation." Ro\al Hart. Sac. Rpf. Intern. Potato Conf., 

 London, Nov. lfi-18, 1921. P. 35-40. 6 figs. 1921. 



''QcANjKR, H. M. New Work on Leaf-Curl and Allied Diseases in Holland. Royal 

 Hort. .Soc. Rpl. Intern. Potato Conf., London, Nov. 1(5-18, 1921. P. 127-145. 20 figs. 1921. 



