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 Californian 
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 many spe- 
