18 THE GEOLOGICAL HISTORY OF PLANTS. 



may have even ascended out of the water in some of their 

 forms. These comparatively simple cellular and tubular 

 structures, now degraded to the humble position of flat 

 lichens or soft or corky fungi, or slender cellular mosses, 

 may have been so strengthened and modified as to con- 

 stitute forest-trees. This would be quite in harmony with 

 what is observed in the development of other plants in 

 primitive geological times ; and a little later in this his- 

 tory we shall see that there is evidence in the flora of the 

 Silurian of a survival of such forms. 



It may be that no geologist or botanist will ever be 

 able to realise these dreams of the past. But, on the 

 other hand, it is quite possible that some fortunate chance 

 may have somewhere preserved specimens of Laurentian 

 plants showing their structure. 



In any case we have here presented to us the strange 

 and startling fact that the remarkable arrangement of 

 protoplasmic matter and chlorophyll, which enables the 

 vegetable cell to perform, with the aid of solar light, the 

 miracle of decomposing carbon dioxide and water, and 

 forming with them woody and corky tissues, had already 

 been introduced upon the earth. It has been well said 

 that no amount of study of inorganic nature would ever 

 have enabled any one to anticipate the possibility of the 

 construction of an apparatus having the chemical powers 

 of the living vegetable cell. Yet this most marvellous 

 structure seems to have been introduced in the full pleni- 

 tude of its powers in the Laurentian age. 



Whether this early Laurentian vegetation was the 

 means of sustaining any animal life other than marine 

 Protozoa, we do not know. It may have existed for its 

 own sake alone, or merely as a purifier of the atmosphere, 

 in preparation for the future introduction of land-ani- 

 mals. The fact that there have existed, even in modern 

 times, oceanic islands rich in vegetation, yet un tenanted 

 by the higher forms of animal life, prepares us to believo 



