RELATION OF EARLY MATURITY TO HARDINESS. 213 



THE RELATION OF EARLY MATURITY TO HARDINESS 



IN TREES. 



BY R. A. EMERSON. 



HARDINESS A MATTER OF HABIT OR OF CONSTITUTION. 



That a tree with well-ripened wood is better able to withstand severe 

 cold than one with immature wood is a matter of common knowledge. 

 A tree which has its leaves and soft, new shoots killed in May by a 

 temperature only a few degrees below freezing might, if well ripened, 

 pass unhurt through a January temperature far below zero Fahrenheit. 

 One would no more question this than that ripe seeds which pass unin- 

 jured through the cold of winter might have been produced by plants 

 as tender as beans or" corn. It is perhaps less commonly known that 

 resistance to cold in trees is due often almost wholly to the habit of 

 early maturity rather than to constitutional hardiness. A concrete ex- 

 ample may help impress the truth of this. Some black walnut trees 

 from northern seed growing at the Experiment Station, by virtue of their 

 perfect maturity, passed through the extremely severe winter of 1898-99 

 without apparent injury, while similar black walnut trees from southern 

 seed, owing to imperfect maturity, have had their new growth killed 

 back from a few inches to two or three feet every winter for the past 

 six years, and yet, notwithstanding this great difference in resistance 

 to cold in winter, a comparatively light freeze late in the spring of 1903 

 killed the new growth of the northern trees just as completely as it 

 did that of the southern ones. All this goes to show that the northern 

 trees were constitutionally no hardier than the southern ones, but that 

 their greater resistance to winter cold was due to their habit of ripening 

 their new growth perfectly in the fall. 



The writer is of course aware that with some plants hardiness to cold 

 is much more a matter of constitution than of habit. For instance, 

 if pea and bean plants, both growing under the same conditions and both 

 equally immature, were exposed to frost, the beans would doubtless be 

 killed, while the peas might be unhurt. But the object of this paper 

 is to show the connection between early maturity and hardiness; hence 

 matters relating to constitutional resistance to cold will be passed over. 

 From a study of relative hardiness of various trees, and through experi- 

 ments aimed to increase hardiness, considerable material bearing upon 

 the relation of early maturity to winter hardiness has accumulated. 

 The most important of the data are presented here. 



EARLY MATURITY AND HARDINESS IN FRUIT TREES A 

 MATTER OF VARIETY. 



Plums. — Peaches naturally grow late in fall and are comparatively 

 easily injured by cold, while our wild plums ripen their wood early and 



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