496 IOWA DEPARTMENT OF AGRICULTURE. 



Many years ago I was convinced by the best of evidence that three-fourths 

 of the losses in Iowa orchards were caused by failure of trees to ripen in the 

 fall before cold weather. The ripening of trees at the proper time in the 

 fall is an important process which fruit growers in Iowa should understand. 



When trees are ready to complete a summer's growth, they withdraw all 

 of the sugar, starch, albuminoids and other nutritive substances from their 

 leaves and other parts where growth is going on, and store them away to be 

 used in starting growth in the following spring. The hardiness of fruit 

 trees in a cold and changeable climate can be determined by their conditions 

 or stages of ripeness after their leaves have been killed by heavy fall frosts. 

 When trees are ripe, all of the carbohydrates (sugar, starch, etc.) which 

 they contain, will be stored in granular form and lignified in their piths and 

 medullary rays. The lignin is used principally by oaks and other trees to 

 prevent their heart wood from rotting, when it is exposed to the weather, 

 and during the ripening process it is used to prevent water from dissolving 

 the grains of starch in ripe trees suddenly during the short spells of warm 

 weather which occur in March and April frequently. Growth can not begin 

 in ripe trees until the grains of starch in their piths are dissolved; but as 

 they are well protected by lignin they can not dissolve, and growth can not 

 begin until after ten or twelve days of continuous warm weather. But when 

 trees do not ripen in the fall no granulated starch can be found in their piths; 

 but sugar, ungranulated starch, etc., could be found in their leaves, un- 

 granulated bark and sapwood. Very short spells of warm weather in March 

 or April would be sufficient to start growth in unripe trees because the dif- 

 ferent kinds of assimilated plant food materials were left when growth was 

 stopped by fall frosts in the right parts of such trees and in proper condition 

 to cause growth as soon as the conditions of the weather would permit it. 



During the ripening process all of the albuminoids in a tree are stored in 

 concentrated form in its buds, where they are well protected by bud-scales, 

 and in its sieve tubes outside of its cambium layer. The sieve tubes of trees 

 are long fibrous vessels of the inner bark, perforated at many points, so 

 that the slimy albuminoids can be forced out of them by pressure from above. 

 Vegetable physiologists tell us that such perforated points on the sieve tubes 

 are closed during their ripening process, to prevent water from coming in 

 contact with the reserve albuminoids; but that they open again when growth 

 begins and the weather becomes warm. But when trees do not ripen in the 

 fall, the perforated points on the sieve tubes remain open during the follow- 

 ing winter and albuminoids in a watery condition could be found at all 

 points of growth in their bodies and limbs. 



Numerous small, light-colored spots are noticeable on the bark of young 

 branches of trees. They are small openings in the bark called cuticles, 

 through which surplus aqueous vapor is discharged from the inside of trees, 

 and through them carbonic acid and other gases are absorbed from the at- 

 mosphere to be used in causing growth. The cuticles are closed during the 

 ripening process in the fall,' but they open again after new growth has com- 

 menced during the following spring. But when trees do not ripen in the 

 fall, their cuticles will remain open all winter and allow the escape of much 

 necessary water. Very cold weather can not injure ripe apple trees, because 

 they are well prepared to endure it. But there have been warm spells of 



