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



induced wore not cataclysmic but gradual, the climate tending 

 ever towards the dry and cold but with innumerable recur- 

 rences of mild and moist conditions temporarily, the ameliorat- 

 ing influences becoming less and less distinct as the Pleistocene, 

 with its climatic rigors, was approached. In the earlier mild 

 and moist period the luxuriant trees of the Sophorere would 

 have been enabled to cross from the Old to the New World 

 and from the New to the Old, in regions beyond the limits of 

 the present tropics, and thus new genera might arise in the 

 tribe which might be common to the New and Old World, and 

 yet be unknown in Australia, which had become isolated before 

 the great differentiation of climate ensued. 



Thus would arise the idea that Australia was separated 

 earlier than America and Africa. Moreover, great land blocks 

 such as America and Western Africa might have effected an 

 interchange of genera and species and thus present likenesses 

 with each other, of a more modern character, than those of 

 Australia with these great land blocks. This of course has 

 reference only to the great tropical groups. With the increas- 

 ing differentiation of climate, the Sophorese retreated more 

 and more to the tropics, but certain hardy forms existed such 

 as the old genus Sophora itself, or other hardy genera were 

 formed, such as Virgilia and Cladrastis. These were the types 

 in extratropical areas which could dispense with the old 

 arborescent stage and the luxuriant foliage, and hence, as the 

 extreme rigors of the Pleistocene arrived, it is noted that the 

 majority of the noble trees of Sophorese vanish, and a herba- 

 ceous type is developed, namely, the Podalyriese of the northern 

 hemisphere. 



The effect of the climate on the ancestors of the Sophorea? 

 and the Podalyriese in the southern hemisphere is more instruc- 

 tive than in the northern hemisphere. In the north the tribe 

 was almost exterminated owing to the excessive climatic rigor 

 of the Pleistocene coupled with the ensuing competition of other 

 and extremely hardy and vigorous types, begotten by the 

 climatic revolution. 



The Podalyriese of the south mark a departure from the 

 Sophoreaa during a great climatic differentiation preceding 

 the separation of Australian from the tropical lands when the 

 flowering plants began to feel the influence of the climatic 

 changes. This land was relatively small and was confined to the 

 tropical and warm temperate regions. It might, therefore, be 

 expected that there would not, on the one hand, be such a great 

 response in genera and species, in the numerical sense, as in the 



