234 ^^^ POPULAR SCIENCE MONTHLY. 



laurels, olives, myrtles, etc. — with their narrow, elongated, coria- 

 ceous, entire or spiny foliage, only slightly divided, do not display 

 the luxuriant fullness of tropical forms, but seem to lead toward 

 them. They touch upon them on some sides, indicating the influ- 

 ence of a special medium, determined by conditions of intermit- 

 tent heat and dryness. A peculiar feature of the Mediterranean 

 group, and one which may help to determine its significance, is 

 the capricious and uneven distribution in the interior region of 

 plants of the most decided characteristics, evidently outside of 

 the range of common species, manifesting affinities with hot coun- 

 try types. These species are narrowly cantoned in certain sta- 

 tions. The Pinus excelsa of the Himalayas is found only on a 

 single mountain of Macedonia ; the Algerine Thuya only in the 

 Atlas ; the false cork-oak in only a few specimens at a single spot ; 

 the carob at a few places on the littoral ; the poplar of the Eu- 

 phrates on the banks of the Jordan and at one point in the prov- 

 ince of Constantine. Numerous instances of this kind betoken 

 the existence of a former condition which has been more or less 

 changed by subsequent events, that the group has suffered from 

 revolutions which have displaced and partly eliminated elements 

 that were formerly more widely distributed. The group has been 

 impoverished, probably by the depreciation of some elements, 

 certainly by the destruction of others. 



This brief review of the forestal zones from north to south is 

 sufficient for the study we have in view of the paleontological 

 origin of the principal types of trees. This origin, which is at 

 the best hard to determine, could not be sought with any proba- 

 bility, except as to those species concerning which we have data 

 of a character to cast light on their history in the past, their for- 

 mer migrations, and their career through time as well as through 

 space. Europe, North America, and the arctic zone furnish these 

 data. They are not to be found in India, China, and Australia, 

 for the guiding thread would be wanting there. Knowledge of 

 many fossils is not enough of itself to conduct to the desired end. 

 Vegetable impressions are useful indications, which, taken singly^ 

 have a relative value, but rarely lead to results of a material 

 bearing. 



Multiplied observations and discoveries, and fossil beds of un- 

 usual richness, to be explored at many points from north to south, 

 have been required to give a view of the floral past of a part of 

 the globe. It was also necessary that these beds, instead of be- 

 longing to a single period, should be frequently separated by long 

 intervals distributed through successive ages, so as to present the 

 complete picture of the series of past times. Thus a comprehen- 

 sive grasp has become possible of the vicissitudes through which 

 the vegetable kingdom has gradually undergone transformation. 



