HORTICULTUKE. 343 



extent, depending upon what part of the twig is used. Based upon tests made 

 in July, it was found that the tenderer varieties which mature a little later in 

 the summer gave the gi'eatest specific gravity a short distance back of the tip. 

 Earlier maturing varieties increased in specific gravity in proportion to the 

 distance from the tip. 



Studies were made of nursery twigs at different seasons of the year and at 

 different temperatures, with the view of determining the extent of correlation 

 of maturity and water content with hardiness. The results of these studies 

 taken in consideration with the data from similar lines of investigation led to 

 the conclusion that the maturity of the wood at the time cold weather sets in 

 has the most important bearing on the ability of the tree to withstand cold. 

 The hardier varieties on the average had a slightly lower moisture content than 

 the more tender varieties, this difference being more marked during the grow- 

 ing season. The more tender sorts evaporate w^ater more readily than do the 

 hardy varieties. After a period of very cold weather the twigs of the hardy 

 varieties are generally foimd to contain the most moisture. 



Studies of the structure of stems in relation to hardiness as conducted by the 

 authors and a number of other investigators show that the rate of evaporation 

 is modified by small differences in thickness and structure of the bark, includ- 

 ing differences in the number of cutinized layers. A lower rate of evaporation 

 in the hardier varieties appears to be due to a denser cell sap. Most of the 

 hardy varieties contain a large amount of starch stored in the pith and medul- 

 lary rays. Forms of M. ioensis, however, proved to be an exception in this 

 regard. 



Studies were also made of the moi'phological differences in apple blossoms as 

 to their correlation with the hardiness of the variety. The results of this work 

 indicate that large thick petals are correlated witl> hardiness, although the con- 

 verse of this is not always true. 



Freezing tests were conducted to determine, if possible, the temperatures at 

 which various twigs will kill under a given condition. All twigs not previously 

 dried were injured to some extent when held in a temperature of — 10° F. for 20 

 minutes. The injury which occurred was found to be inversely proportional to 

 the hardiness of the variety. Even those varieties which can withstand from 

 — 25 to — 40° under natural conditions can not withstand a sudden drop in tem- 

 perature to even — 10° ; from which it is concluded that a sudden drop in tem- 

 perature is more injurious than the actual degree of cold. 



With reference to the results of their investigations as a wfeole the authors 

 conclude that " while in the various lines of comparison which were made there 

 were found many indications of morphological differences between hardy and 

 tender varieties, yet from the practical viewpoint it is impossible as yet to name 

 any one test by which the degree of constitutional hardiness of a seedling apple 

 may be foretold. Among the various tests for hardiness, that of the length of 

 season required by the tree to mature the season's gi-owth is of first importance. 

 Perhaps by taking careful notes on a number of trees of any particular variety 

 for two or three years or more, noting their time of starting and cessation of 

 growth, their ability to produce a good root system from the scion, their water 

 content, the resistance of their twigs to sudden zero temperatures, and their 

 rate of evaporation, a pretty accurate idea of the ability of the tree to withstand 

 cold might be obtained. If, in addition, the variety has hard wood, a good 

 amount of stored starch, and large petals, these would be further indications of 

 hardiness, although from this study it appears that these points are of less 

 importance than those first named." 



A special apparatus used in making mechanical tests of small twigs is illus- 

 trated and described. References are given to related studies on hardiness. 



