82 State Horticiilfiiral Society. 



instance, all produce pale, yellowish-green twigs, and they are remarkablv 

 hardy. Their fruit buds frequently pass the winter safely and the 

 trees produce fruit when other varieties are winter killed. The Ortiz, 

 another variety with pale, yellowish-green twigs, is remarkaljly hardy, 

 while varieties containing darkest purple twigs winter kill. An examina- 

 tion of the fruit buds of various varieties during a number of winters 

 indicates that the hardiness of these varietfes producing pale twigs is 

 due to the fact that they arc less easily stimulated into growth on warm 

 winter days and consequently remain more thoroughly dormant during 

 winter than do those sorts which possess dark purple twigs. 



Experiments have shown why this may be. Thermometers inserted 

 m the twigs of ver}^ purple colored varieties show that on sunny days in 

 v.inter these twigs often attain a temperature of fifteen or sixteen degrees 

 higher than the temperature of the atmosphere. Laboratory experiments 

 show that this purple coloring matter of the twig or syanin, has the power 

 of absorbing great quantities of heat from the sun. Similar thermometers 

 inserted in peach twigs whitened with lime wash to retiect the rays of the 

 Lun, show that the whitened twigs will remain at atmospheric temperature, 

 or slightlv below. It mav easilv be seen, that during sunn\- winter davs a 

 raise of fifteen degrees, or sometimes even more than twenty degrees, 

 in the temperature of the purple twigs above the atmospheric temperature, 

 might cause them to make considerable growth and become active enough 

 to be easily injured by the subsequent cold, while twigs which are 

 whitened to reflect this heat, remaining at the atmospheric temperature, 

 might pass this sunny period in a dormant condition. The varieties like 

 the Snow and Ortiz, which have pale twigs, register a temperature be- 

 tween that of the whitened twigs and the dark purple twigs, showing 

 that thev would probably be less easily stimulated into growth on sunny 

 days than would the latter. Aside from the difference in actual tem- 

 perature of light twigs and the dark purple twigs, the "rapid change, or 

 fluctuation, in temperature of the latter may be unfavorable. Observa- 

 tions show that in cases where the difference between day and night tem- 

 perature of the atmosphere and of whitened twigs is only ten degrees, 

 that the difference between the night and day temperatures of purple 

 twio-s was twenty-five or twenty-six degrees. Tn days of intermittent 

 sunlight, the sudden appearance of the sun from behind a cloud in one 

 case where the ground was covered with a light snow which reflected 

 the heat upwards to the trees, thermometers in purple twigs raised in 

 temperature sixteen, degrees in six or seven minutes; when the sun 

 again passed under a cloud, the temperature of the twig fell fifteen or 

 sixteen decrees in a verv few moments. This fluctuation of temperature 

 on the part of the purple twigs is no dobut injurious. 



