1920] The Earliest Known Land Flora 133 



WEEKLY EVENING MEETING, 



Friday, April 30, 1920. 



J. H. Balfour Browne, K.C. D.L. J.P. LL.D. Vice-President, 

 in the Chair. 



F. 0. Bower, Pres.E.S.E. Sc.D. LL.D. F.R.S., 



Regius Professor of Botany, University of Glasgow. 



The Earliest Known Land Flora. 



The Vegetable Kingdom is made up of plants of most varied size, 

 character and habitat. Comparing those various types, the view 

 becomes ever more insistent that dependence on water is the master- 

 factor determining their existence. As we range their diverse forms 

 according to probable sequences of descent, those which we regard as 

 the most primitive according to their structure and mode of repro- 

 duction are those which are habitually the most dependent upon 

 constant water supply. It is the same with the Animal Kingdom. 

 These broad results were summed up by Weismann some forty years 

 ago in the statement that the birth-place of all animal and plant life 

 lay in the sea. If this be true, it follows that all life on exposed 

 land-surfaces has been secondary, and derivative. 



Geologists tell us that from the remotest past land-surfaces have 

 stood exposed above the level of the ocean. The continents and 

 islands may have differed from time to time in their outline and area 

 from those of the present day. But we may believe that from the 

 earliest period land-surfaces have had a continuous existence, so that 

 life upon land may itself have been continuous from the time when 

 living organisms first emerged from their natal waters. Such beliefs 

 throw back to the very remote past the possible origin of life upon 

 dry land. But still the probability remains that aquatic life ante- 

 dated that event. These considerations lead inevitably to the 

 questions : AVhen was dry land first invaded from the water ? What 

 were the first land-living plants and animals like ? And how did 

 they rank as compared with modern life ? 



Leaving zoologists to solve these questions for their own branch, 

 we botanists are to-day in a better position than ever before to 

 answer them with regard to plants. Though still far from being- 

 able to visualize the beginning of the story, recent discoveries have 

 made it possible to see clearly and in detail the nature of the earliest 

 known land flora, which is that of the Lower Devonian Period. 

 During recent years fossil plants of the Lower Devonian have been 



