336 



BOTANY 



Scale-leaves. Besides the typical foliage-leaves, scale-leaves, which are 

 purely protective and quite destitute of chlorophyll, are of common occurrence. 



These are especially well developed 



sc 



,st 



in the Pines and Firs, where the 

 winter-buds, terminating each sea- 

 son's growth, are completely covered 

 by them. Similar protective leaves 

 usually enclose the young flowers. 



Branching 



All of the Coniferae branch 

 freely, and owing to the persist- 

 ence of the terminal bud, both 

 in the main axis and the lateral 

 shoots, the trees are exceedingly 

 symmetrical in form. A bud 

 may be formed in the axil of 

 each leaf, but only a small pro- 

 portion of these develop. In the 

 Pines, while buds are formed in 

 all the axils of the leaves of a 

 shoot, only a small number, 

 developed just below the ter- 

 minal bud, give rise to the 

 branches, which thus are ar- 

 ranged in circles, the successive 

 circles being separated by inter- 

 nodes representing a season's 

 growth. This is still more 

 marked in Araucaria. In case 

 the terminal bud is destroyed, 

 one of the lateral branches below it grows upright and takes its place. 

 In a few species e.g. Pinus Sabiniana the main axis very early 

 ceases its growth, and the tree is widely branched, and the same thing 

 occurs in some other species as they grow old. This is seen in the 

 Italian Stone-pine (P. pinea), P. rigida, and other species. Adven- 

 titious buds are developed in some forms, this being especially con- 

 spicuous in Sequoia sempervirens. 



The Root 



The tap-root of the young sporophyte is usually replaced by numer- 

 ous lateral roots, which often spread horizontally for a long distance. 



The young root shows a central plerome-cylinder, covered with a common 

 initial layer of tissue from which the other tissues are developed. The primary 

 root is diarch in most forms, but in the Abietinese, where the number of coty- 

 ledons is more than two, the number of primary xylem-masses in the root is 

 more than two (Fig. 307, G), although not necessarily as many as the coty- 



m 



FIG. 229. Pi mis Coulteri. A, section of 

 leaf (X 35) ; r, resin-ducts in the green 

 mesophyll; st, stomata; sc, hypoder- 

 mal masses of sclerenchyma ; the two 

 vascular bundles lie in the central color- 

 less area. B, stoma, and surrounding 

 tissues (x 400) ; sc, sclerenchyma; i, 

 air-space below the stoma; m, meso- 

 phyll-cells. 



