No. 464.] STUDY OF THE SALICACEE. 525 
This idea is emphasized more particularly in the case of the 
willows by the observation that Salir protefolia has no less than 
four variants, or five forms in all, as presented by the generally 
accepted specific type and the varieties designated as flexuosa, 
lanceolata, linearifolia, and longifolia — forms which are all 
characteristic of the Dakota group, though S. protefolia and S. 
protafolia flexuosa are also found in the lower Cretaceous. We 
therefore find that so far as the geological evidence alone is con- 
cerned, it throws no light whatever upon the possible ancestry 
of these plants, it affords absolutely no clue as to their relations 
to other groups of plants, and it gives no very trustworthy 
information as to their present position in the scale of develop- 
ment. But when such evidence is taken in conjunction with 
that derived from a knowledge of the family as at present 
existing, the following conclusions appear to be fully justified : 
(1) The Salicacez as a whole is an Old World family with 
its probable center of distribution in southeastern Europe and 
Central Asia. 
(2) It is a family with a strong tendency to a boreal habit 
which has become more definitely emphasized since Tertiary 
time. 
3). The present tropical and subtropical members of the 
family, probably represent the relics of a wider dispersion in 
Cretaceous and Tertiary time, which have been isolated and 
localized as the result of more recent contraction in the family 
as a whole. 
(4) The family at present affords strong proof of a temperate 
climate. In Cretaceous time it was compatible with a much 
warmer climate than at present, as indicated by the survival 
of tropical and subtropical forms; but changes more recently 
effected, have made its tendencies boreal rather than tropical. 
(5) The family had but a feeble development in the Lower 
Cretaceous, but become greatly augmented in the Middle Cre- 
taceous. 
(6) Itis a family which may be regarded as still in process 
of development. 
(7) The process of victi. is chiefly expressed in the 
genus Salix which shows a very great increase since the Middle 
Cretaceous. 
