PAST HISTORIES OF PLANT FAMILIES 85 



Hence it is wise to be very cautious about drawing 

 any important conclusions from the relative numbers of 

 the different species, or the absence of any type of plant 

 from the lists of those as yet known from the Cretaceous. 

 When quantities of structurally preserved material can 

 be examined containing the flowering plants in petrifac- 

 tions, then it will be possible to speak with some security 

 of the nature of the Mesozoic flora as a whole. 



The positive evidence which is already accumulated, 

 however, is of great value, and from it certain deductions 

 may be safely made. Specimens of Cretaceous plants 

 from various parts of the world seem to indicate that 

 there was a very striking uniformity in the flora of that 

 period all over the globe. In America and in Central 

 Europe, for example, the same types of plants were 

 growing. We shall see that, as time advanced, the vari- 

 ous types became separated out, dying away in different 

 places, until each great continent and division of land 

 had a special set of plants of its own. At the com- 

 mencement of the reign of flowering plants, however, 

 they seem to have lived together in the way we are 

 told the beasts first lived in the garden of Eden. 



At the beginning of the Tertiary period there were 

 still many tropical forms, such as Palms, Cycads, Nipa, 

 various Artocarpacees, Lauracecs, Araliacece, and others, 

 growing side by side with such temperate forms as 

 Quercus, Almis, Betula, Populus, Viburnum, and others 

 of the same kind. Before the middle of the Tertiary 

 was reached the last Cycads died in what is now known 

 as Europe; and soon after the middle Tertiary all the 

 tropical types died out of this zone. 



At the same time those plants whose leaves appear 

 to have fallen at the end of the warm season began to 

 become common, which is taken as an indication of a 

 climatic influence at work. Some writers consider that 

 in the Cretaceous times there was no cold season, and 

 therefore no regular period of leaf fall, but as the 

 climate became temperate the deciduous trees increased 



