10 ELEMENTARY FORESTRY. 



have a more compact root system than those grown on poor 

 land. 



At the Minnesota Experiment Station a small Bur Oak 

 growing on dry, gravelly soil had a tap root that was evi- 

 dently 20 feet long 1 , while on moist fertile clay land in the 

 same section such trees probably seldom have tap roots more 

 than six feet long. 



Buds are placed regularly on the young branches and are 

 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 de- 

 velop into flowers and fruit, and leaf buds which develop 

 into leaves and branches. These can generally be distin- 

 guished from each other by their shape and size and by cut- 

 ting through them and noting their construction. Flower 

 buds are generally more liable to injury from climatic changes 

 than leaf buds. 



The Leaves of our trees vary much in size and shape. They 

 are simple when composed of but one piece as the 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 en- 

 tire foliage yearly while our so-called evergreen trees lose a 

 part of their leaves each year. The length of time leaves re- 

 main on this latter class of trees varies from two or three 

 years, in the case of White Pine growing in very severe loca- 

 tions in this section, to perhaps eight years, in the case of 

 Red Cedar favorably located. The time that leaves remain 

 on the branches in the case of evergreens depends to some ex- 

 tent 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: 



