SEED PLANTS 167 



our northern forests, and while a much more ancient 

 type than the Angiosperms, they are still a predominant 

 type of vegetation in many regions, where the forests are 

 often composed almost exclusively of these trees. In 

 contrast to the Cycads, which rarely attain tree-like 

 proportions, and whose leaves are large and fern-like, 

 the Conifers usually become trees, often of gigantic size, 

 and in most of them the leaves are small and needle- 

 shaped. In the relation of stem and leaves the Coni- 

 fers recall the club-mosses, while the Cycads are very 

 much like the ferns, and it is not impossible that this 

 may indicate an entirely independent origin for the 

 two groups from Lycopods and ferns respectively. The 

 recurrence of fossil forms of an intermediate character 

 supports such a hypothesis. 



The sporophyte in the Conifers, as already stated, is 

 always large, usually becoming arborescent, and some- 

 times a hundred metres and more in height. These 

 giant trees reach their greatest development on the 

 western slopes of the mountains of Pacific North 

 America, where a number of species attain a height of 

 one hundred metres, or it is claimed one hundred and 

 fifty metres, with trunks from five to six metres in 

 diameter; or, in the case of the great Calif ornian 

 Sequoias, ten metres or even more. The extraordi- 

 nary height of coniferous trees, which almost always 

 exceeds that of their deciduous companions, is due to 

 the persistence of the original apical bud, which, unless 

 injured by accident, remains active, so that a definite 

 central axis is formed which may grow in length for 

 hundreds of years. The regular whorls of branches 

 formed at the base of each year's growth in manj' spe- 



