330 STRUCTURE OF PIXALES 



embryo, or sprouting of the seed, is often erroneously termed the 

 germination of the seed. 



The maidenhair tree. Ginkgo biloba, a native of China and 

 Japan and now extensively cultivated throughout the world, is 

 the sole survivor of another ancient order of gymnosperms that 

 have man}- points in common with the cycads and ferns. The 

 tall shaft of the stem, wide-spreading branches and the arrange- 

 ment and character of the tissues is more suggestive of the next 

 order, the cone-bearing trees. The leaves, however, are fern- 

 like in appearance and are deciduous, unlike most of the Gymno- 

 spermae. The arrangement of the sporangia, the development 

 of the gametophytes, and fertilization are of the same nature 

 as in the cycads. It is noteworthy that fertilization may be 

 effected after the megasporangia have fallen, thus approaching 

 the condition seen in Selagiuclla. 



121. Order b. Pinales or Cone-bearing Trees. — This order is 

 by far the largest group of gymnosperms and includes our well- 

 known evergreen or cone-bearing trees. They are largely confined 

 to temperate regions and are more numerous in the northern than 

 in the southern hemisphere. The shores of the Pacific are espe- 

 cially favorable for their development and on our western coast 

 they attain dimensions equalled only by the giant Eucalyptus of 

 Australia. Though less ancient in origin than the cycads, they 

 have declined in the same way as the latter order and only a 

 remnant of this very extensive group survive today. However, 

 their variations have been more beneficial than in the case of the 

 cycads and as a result nearly 300 species are adapted to present 

 conditions upon the earth and constitute an important part, and 

 commercially the most valuable part of our forest "vegetation. 



(a) Structural and Adaptive Features of the Pinales. — One 

 of the variations that is of great benefit to many of these plants 

 is their habit of forming buds (sec page 97). which appear in 

 this order in more perfect form than any of the preceding. By 

 means of the scale leaves of the buds all the organs that are to 

 be produced each season are protected against drying winds. 

 The terminal bud of the tree is frequently the most vigorous and 

 as a result spire-like stems with very symmetrically arranged 



