358 



GENERAL MORPHOLOGY OF PLANTS 



trees of large size widely distributed over different parts of the 

 world, especially the Northern Hemisphere. Many of these 

 grow in great abundance in extreme northern latitudes where 

 the winter season is very cold, while others occur in temperate 

 and in subtropical countries where the heat of the season is often 

 very great. Some of the trees of great size are the giant red 

 woods (Sequoia) -of the Sierra Nevada Mountains. Others are 

 the pines, spruces, firs, balsams, larches, cypresses, cedars, hem- 

 lock spruces, arbor vitae, etc. The American yew or ground 

 hemlock is an example of a shrubby form. The majority of the 

 conifers have a straight excurrent trunk, with lateral rather subor- 

 dinate branches, thus forming a large straight boll, making them 

 especially valuable as timber trees, aside 

 from the valuable quality of many of 

 the woods. The branches in the pines, 

 balsams, and some other trees, arise in 

 apparent whorls on the main shoot, 

 from lateral buds grouped just below 

 the terminal bud. It is possible then 

 to determine the age of the tree so 

 far as the branches are retained over 

 the lower part of the trunk. In the 

 hemlock spruce, cedars, and some others 

 the branches are more or less scattered 

 along on the trunk. 



526. The leaves are needle-like and 

 quite long in the pines, shorter and 

 more flattened in the spruces, and scale- 

 like in the cedars, arbor vibe, etc. In 

 the pines they are in clusters of two 

 to five (rarely one in some western 

 Pines) at the end of a very short branch. 



Q k ; nds Q f 



Fig. 342. 



wood-cells. X 3 2 5 . (After Sachs.) 



developed each year, the long ones and the short ones. The long 

 ones correspond in arrangement on the stem to the short ones 

 and this is the reason they are so crowded on the stem as to 



