364 THE . SPERMATOPHYTES 



THE CONIFERS 



349. The conifers. This group (order Conifer ales) has repre- 

 sentatives distributed all over the earth, some of them forming 

 the most extensive forests and having the greatest value as 

 timber trees. There .are not many more than 300 species of 

 conifers, of which the pines (Pi-mis) have 70; Podocarpus 

 (growing in South America and eastern Asia), 40 ; the junipers 

 (Juniperus), 30; certain cedars (Cupressus), 20; the firs (Abies), 

 20; and the spruces (Picea), 12. Others have few species and 

 a very limited distribution. Such a form is the giant redwood 

 of California (Sequoia gigantea), which is found only in a few 

 scattered groves in the Sierra Nevada Mountains (Fig. 33). 



350. The form and foliage of the conifers. The form and 

 foliage of the conifers is generally very characteristic. The 

 trees have, as a rule, a single central stem which rises vertically 

 from the ground, and the side branches spread out horizontally 

 from this shaft so that the trees are very symmetrical and taper 

 to a point like a cone. The foliage, as a rule, consists of scale- 

 or needle-shaped leaves, which usually remain on the trees for 

 a number of years so that most of the trees are evergreen. But 

 there are some exceptions to the rule, as the larch or tamarack 

 (Larix), which sheds its needles 'every year. 



The needle leaves can endure severe cold, fierce heat, and 

 drought. This is made possible by their very compact structure 

 (Fig. 296), which presents a minimum of surface exposure and 

 the protective layer of thick-walled cells under the heavy epider- 

 mis. The chlorophyll-bearing tissue is closely packed in the pine 

 leaf and consists of cells with peculiar infolding walls. Some 

 species of pine have needles with one fibre-vascular bundle, e.g. 

 the white pine ; others have two bundles, e.g. the Scotch and 

 the Austrian pine. The buds, leaves, and stems contain much 

 resin and turpentine, which render them unpalatable to grazing 

 animals and cover them with a film which sheds water and 

 protects the plant both from the winter's cold and the summer's 



