Dispersal of Herbaceous A ngio sperms. 599 
Australasia. This connexion seems rather to have been by a series of 
large islands than by a continuous land bridge. 
19. A hypothetical reconstruction of the ancient flora of Antarctica 
indicates that nearly two-thirds of its ‘ endemic ’ dicotyledons were woody 
plants. 
20. The chief factor in the development of herbs has been the pro- 
gressive refrigeration of climate in the temperate zones during the Tertiary 
period. This probably was effective in gradually stunting woody plants 
more and more until their aerial portions persisted only for a single growing 
season. The annual herb seems to be the most recent type. Most families 
which are able to withstand cold in the form of trees and shrubs have 
produced few or no herbaceous members. 
a 1. The great majority of herbs were probably developed in the land- 
mass of the north temperate zone, and arose first in the mountains. Herbs 
have also been produced in mountainous regions in the tropics and the 
southern hemisphere. Many tropical lowland herbs have descended from 
the mountains. Others have been evolved under tropical conditions in 
response to the alternation of wet and dry seasons or for other causes. 
Many herbs in desert or dry regions have likewise arisen in response to 
discontinuity in the amount of moisture. A large body of plants, particularly 
in the tropics, have become herbaceous and semi-herbaceous through an 
assumption of the climbing habit. Most herbs seem to have appeared 
during the Tertiary, many of them probably not till the latter part of the 
period, but it is likely that in rare cases, under adverse climatic conditions, 
they were present in the Cretaceous. 
The writers wish to express their sincere thanks to the authorities of 
the Arnold Arboretum and of the Gray Herbarium, of Harvard University, 
for frequent use of their libraries and collections ; and to Professors 
H. C. Ernst and S. B. Wolbach, of the Harvard Medical School, for loan of 
their photomicrographic apparatus. 
Bibliography. 
1. Adkinson, J. : Some Features of the Anatomy of the Vitaceae. Ann. Bot., vol. xxvii, 1913. 
2. Bailey, I. W. : The Relation of the Leaf-trace to the formation of Compound Rays in the 
Lower Dicotyledons. Ann. Bot., vol. xxv, 1911. 
3. an d Sinnott, E. W. : Anatomical Evidences of Reduction in certain of the 
Amentiferae. Bot. Gazette, vol. lviii, 1914. 
4. Darwin, C. : The Origin of Species. 6th ed. 
5. Eames, A. J. : On the Origin of the ILerbaceous Type in the Angiosperms. Ann. Bot., vol. xxv, 
