270 POMOLOGY 



tion that might exist between the wood structure or other 

 morphological characters and the hardiness of plants. Hal- 

 sted ^ made a special investigation and reported that "No 

 constant difference in all structures probably exists among 

 apple twigs by means of which one sort may be umnistak- 

 ably distinguished from all others. Much less is there any 

 point in minute structure invariably present with those sorts 

 which are classed as hardy and absent from tender vari- 

 eties. Maturity of twigs is a condition of successful win- 

 tering, and therefore the so-called hardy sorts are quite sure 

 to finish their seasons' growth before autumn frosts arrive." 



More recently Beach and Allen ^ conducted some exten- 

 sive investigations on this problem, and observed a large 

 number of plant characters of hardy and tender varieties of 

 fruits. In general, no outstanding and consistent correla- 

 tions could be found, but they report that "The hardier 

 varieties on the average had a slightly lower moisture con- 

 tent than the more tender varieties," also "Large, thick 

 petals are correlated with hardiness, although the converse 

 of this is not always true." 



240. Influence of type of soil. — Inasmuch as the type of 

 soil materially influences the maturity of the trees, this 

 factor becomes one of importance in studying winter injury. 

 In general, a soil that is heavy and inclined to be wet will 

 delay maturity and hence, other things being equal, there 

 would usually be more winter injury on such a soil than on 

 one of a lighter nature. This is particularly true of the sub- 

 soil, as indicated in Chapter VII. Bouyoucos ^ has shown 

 that a heavy soil contains more moisture and will not freeze 

 so deeply as a lighter one, although a sand or gravel will 



1 Halsted, B. D. Iowa Agr. Exp. Sta. Bull. 4. 1889. Mem. Torrey 

 Bot. Club, 2: 1, 26. 



2 Iowa Agr. Exp. Sta. Res. Bull. 21. 1915. 



3 Bouyoucos, G. J. Mich. Agr. Exp. Sta. Tech. Bull. 26, 1916. 



