DEVELOPMENT OF PLANTS 347 



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 many 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 are 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 Selaginella. 



121. Order b. Finales 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 con- 

 fined to temperate regions and are more numerous in the northern 

 than in the southern hemisphere. The shores of the Pacific are 

 especially favorable for their development and on our western 

 coast they attain dimensions equalled only by the giant Eucalyp- 

 tus 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 survives 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 Finales. — One of 

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

 is their habit of forming buds (see page 66), 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 



