PLANTING AND CARE OF TREES 41 



flowers a bud is capable of producing is determined not during the 

 spring elongation of the bud but during its formation the previous 

 3^ear. At least a single bud is usually formed above each leaf. Of 

 all the buds produced in a season only a very small number ever 

 start and grow into branchlets, and the great majority of these 

 branchlets eventually die and are pruned off by the tree. There 

 is a struggle for existence among buds and branchlets as well as 

 among seedlings, and the strongest alone survive. The accompany- 

 ing diagram (fig. 21) shows the condition that might result from 

 a free development of buds and branches in contrast with the con- 

 dition that usually exists. Dormant buds frequently retain their 

 vitality for many years and may be forced into development if 

 the growth above them is injured. Adventitious buds are those that 

 form outside of their regular position at the nodes. They are 

 responsible for the sprouts that regularly fonn on the cut stump 

 of Chestnut and many other of our deciduous trees. Poplars and 

 Willows (p. 351) produce them in abundance when the limbs 

 are cut back or ^^pollarded." 



The bud-scales are modified leaves which protect the parts with- 

 in from mechanical injury and from loss of moisture, but except 

 for the prevention of sudden changes of temperature, they are of 

 little value as a protection against cold as is so often supposed. At 

 fallirig they leave a ring or band of scale-scars marking the limit 

 of each yearns growth. These bands often remain distinct for 

 many 3- ears (see twig of Beech p. 295) and by counting their number 

 the age of the branchlet may be estimated. Thus it can be readily 

 seen that the figure of the Horse-chestnut represents growth made 

 during three years. Each 3'ear a ring of new Avood is formed just 

 underneath the bark, and a count of the number of these annual 

 rings between the central pith and the bark, as seen in a cross 

 section of a branch or trunk, will likewise give the age of the part 

 investigated. The uppermost buds of a year's growth are gen^ 

 erally the largest and most likely to develop into branches the 

 following spring. In some species, as many of the Evergreens, 

 and the Carolina Poplar (p. 261) for example, the branches com- 

 ing from these more vigorous buds form regular whorls along the 

 trunk at the upper part of each year's growth and afford for such 

 species a third means of estimating the age. 



