598 
Sinnott arid Bailey. — The Origin and 
little immigration from the south since the retreat of the ice. Its general 
composition as to proportions of herbs and woody plants is probably much 
the same as it was during glacial time. It consequently furnishes us with 
an indication of what the climate of Europe was like during the Ice Age, 
since there is in general a rather close agreement between the minimum 
temperature of a region and the percentage of herbs in its flora. 
13. The endemic plants in a flora are usually to be regarded as its 
most ancient element. Herbs, however, from the brevity of their life- 
cycles, are apt to become modified more rapidly than woody plants, and 
hence may be developed into endemic types in a comparatively short time. 
Endemic trees or shrubs are almost always very ancient. 
14. In various oceanic and continental islands which are believed 
to possess faunas and floras of considerable antiquity, the most ancient 
element in the vegetation — the species of the endemic genera — is almost 
entirely composed of woody plants ; the next younger, the endemic species 
of non-endemic genera, shows a larger proportion of herbs ; and the non- 
endemic species, presumably the most recent element, are overwhelmingly 
herbaceous. 
15. The continental areas of the southern hemisphere are also believed 
to retain many ancient types of animals and plants. In these regions, as 
in isolated islands, the most ancient part of the vegetation is overwhelm- 
ingly woody and the more recent mainly herbaceous. 
16. These facts point to the conclusion that the ancient flora of the 
world was for the most part composed of woody plants, and that the 
majority of herbs, originating comparatively recently in the land-mass 
of the north temperate zone, have spread thence over most of the 
earth. 
17. This recent entrance of northern plants into the Antipodes has 
mainly been along the Himalayas, the Andes, and the African highlands. 
These invasions have been almost entirely of herbs, which from their ability 
to migrate rapidly and to withstand adverse conditions have become the 
most ubiquitous and' aggressive type of vegetation, and constitute practically 
all plants known as weeds. 
18. The recent date of the invasion of the south temperate zone 
by these northern herbs has a bearing on various problems of geology and 
climatology, such as the periods of direct lowland or mountain-chain con- 
nexion between the northern continents and Australasia, South America, 
South Africa, and Madagascar ; the climate of these regions during the 
Tertiary ; and the extent and climate of the Antarctic continent. The latter 
question is perhaps the most important. The distribution of these northern 
plants and of the ‘ endemic ’ Antarctic flora can well be explained only on 
the assumption of the recent existence of a temperate Antarctic continent 
which was more closely connected than at present with South America and 
