14 ELEMENTARY FORESTRY. 



said to be either alternate or opposite. When they occur on the 

 stump or on roots they are not arranged in any regular order. 

 There are two kinds of buds flower buds, which develop into 

 flowers and fruit; and leaf buds, which develop into leaves and 

 branches. These can generally be distinguished from each 

 other by their shape and size and by cutting through them and 

 noting their construction. Flower buds are generally more lia- 

 ble to injury from climatic changes than leaf buds. 



The I/eaves of our trees vary much in size and shape. They 

 are simple when composed of but one piece, as ihe leaves of 

 the Oak, Maple and Birch, and compound when composed of 

 more than one piece, as the leaves of the Locust, Ash and Black 

 Walnut. Leaves are made up of a framework filled in with 

 cellular tissue and covered with a thin skin. This skin has very 

 many small pores in it called stomata, through which the plant 

 takes in carbon dioxide from the air and gives off oxygen and 

 water. 



All our trees shed at least a part of their leaves each year. 

 All the broad-leaved trees and the Tamarack shed their entire 

 foliage yearly, while our so-called evergreen trees lose a part 

 of their leaves each year. The length of time leaves remain on 

 this latter class of trees varies from two or three years, in the 

 case of White Pine growing in very severe locations in this 

 section, to perhaps eight years, in the case of Red Cedar favora- 

 bly located. The time that leaves remain on the branches of 

 evergreens depends to some extent on the location and age of 

 the individual tree. 



The following table gives the approximate length of time 

 that leaves of conifers remain on trees in Minnesota: 



