222 MORPHOLOGY OF GYMNOSPERMS 



and the Pacific islands). The group is a very natural one, practically 

 restricted to the southern hemisphere, and very distinct from the other 

 tribes. 



It is evident that it is impossible to include so many diverse forms 

 in one continuous account. The tribes will be considered together 

 when the characters justify it; but in many cases they must be treated 

 separately. 



I. The vegetative organs 



The most conspicuous feature of the body of most of the Pinaceae 

 is the central shaft, giving rise to a series of wide-spreading branches 

 (figs. 252-254). In size the Pinaceae range from small shrubs to the 

 largest trees. The "big trees" of California {Sequoia gigantea) 

 attain a height of 95 meters, with a diameter of 10 meters; but 

 in diameter the "big tree of Tule" (Taxodium mucronatum) in 

 southern Mexico far surpasses even the largest sequoias, for it has 

 reached the surprising diameter of 17 meters (fig. 255). The 

 branches are dimorphic, the two forms being characterized as long 

 shoots and dwarf (or spur) shoots. In some forms both kinds of 

 shoots bear foliage leaves; but in Finns the long shoots bear only 

 scale leaves, while the dwarf shoots bear the only foliage leaves. In 

 Sciadopilys the condition of Pinus obtains, except that the dwarf 

 shoot is apparently replaced by the peculiar double needle leaf. 



In the seedlings a very different behavior of the shoots may be 

 observed. These juvenile forms are usually very transient, but they 

 may be "fixed" by culture, so that the plant assumes a permanent 

 appearance very different from its ordinary adult form. Goebel 

 (58) has given an interesting resume of this subject. For example, 

 in Pinus the long shoots of seedlings bear foliage leaves, which may 

 disappear from the long shoots in the second year, as in P. silvesiris, 

 or may continue for many years. These needle-like primary' leaves 

 are of simpler anatomical structure than the subsequent foliage leaves, 

 especially in the matter of provision for controlling transpiration. In 

 the juvenile forms of Larix the leaves persist during the winter, and 

 even in adult trees the juvenile characters may appear in first-year 

 shoots from adventitious buds, as we have observed also in Thuja 

 occidentalis (fig. 256). It is among the Cupressineae, however, that 



