224 E. C. Andrews — The Geological History of the 



development. Owing- to these and other causes they were 

 forced north and south of the tropical and subtropical lands. 

 This had been the history of the Coniferse also about the same 

 time, or perchance, at an earlier period. 



In the southern lands Fagus appears to have established 

 itself firmly, although there was a wholesale extinction of 

 amental types there either at this or a later period. Casuarin- 

 acea>, however, is one of the families which sprang from an 

 early form, by adapting itself to the hungry and barren sandy 

 soils in the warmer portions of Australia. One of the most 

 serious handicaps which had been imposed upon the Coniferae 

 and the Amentales was the peculiarity of their constitution, 

 whereby only with the greatest difficulty were they enabled to 

 reduce their size as individuals. This inability to reduce the 

 great size of their woody stems brought about the extinction 

 of very many genera, and, perhaps, even families, during the 

 great zoning of the climate. The Casuarinacese offset this 

 inherent defect in the family constitution by reducing the leaf 

 surface and by sending down long roots to tap the under- 

 ground sources of moisture, and, moreover, this type succeeded 

 also in life by following watercourses, swamps, and other 

 supplies of moisture, such as occur on the sides of mountains 

 formed of porous or well-jointed sediments or sandy rocks. 



But during the second great differentiation in the northern 

 hemisphere the Amentales became very vigorous especially as 

 the Glacial Period was approached. During this post-Eocene 

 Period, Quercus, Salix, and other types increased in numbers 

 and began to advance south. Especially qualified were these 

 grand types for the conquest of cold well-watered regions after 

 their development of the deciduous habit, whereby they could 

 rest in the winter. In the far south Fagus only succeeded in 

 facing the cold by reducing the leaf surface, by the crowding 

 together of individuals and by keeping in the shelter of moun- 

 tains as much as possible. Fagus moorei, in the northern por- 

 tion of New South Wales, has a large leaf suggestive of the 

 earlier more luxuriant amental leaf. The Casuarines on the 

 other hand, are striking examples of the extreme reduction of 

 leaf surface. The one exhibits in a marked degree an adapta- 

 tion to a cold, moist, but sheltered area, the other exhibits in 

 an equally marked degree an adaptation to poor hungry soils 

 and to a climate showing marked diurnal changes of climate. 



Alnus. In South America Alnus is to be explained, prob- 

 ably, as a southern immigrant during the great Glacial Period, 

 although it is possible that it migrated to South America and 



