1894.] The Meaning of Tree-Life. 467 
character of its continents. : The surcharging of the atmos- 
phere with water-vapor meant excessive precipitation, and the 
shallow-water conditions obtaining around the continental 
islands, together with the probable lowness of these isolated 
landmasses favored the existence of extensive swamps and 
marshy flats, in which the water may have been either fresh 
or brackish. Here jn these primordial swamps the vegeta- 
tion destined to cover the earth made its determined struggle 
for existence. On the higher land there was too much heat; 
in the seas there was too much water; in the swamps was the 
: requisite combination of water, heat, and heavy carbon-laden 
; air. Under such conditions the first types that took possession 
: must have spread and multiplied with incredible rapidity- 
; What followed? Inevitably the primitive low-growing plants 
a crowded closer and closer together and became a rank tangle 
of growth; where there had been at first plenty of room for 
q every individual to spread, there were how maby struggling 
4 for the mastery of each square foot of swamp. All hada foot- 
hold in the earth but only the few that stood the highest could 
| drink in the feeble rays of the cloud-bedimmed Silurian sun- 
= shine. Then the real battle for the light began in earnest, the 
stronger against the weaker, the older established types against 
the newer ones whose foot-hold was less certain; higher and 
higher the rank swamp-growth rose, all its members struggling 
together for the light and open air. And so in the wierd gigantic 
club-mosses of those far-off times wesee the prophetic beginnings 
of the tree-life of to-day; and to trace the development of the 
majestic forests of the present from those dank swampy jungles 
of the past is the problem before us. It would seem at first 
glance that in the primeval jungle “ might made right,” if ever 
it made it anywhere. But no! the “ survival of the fittest” 
worked in two directions. Vegetative luxuriance was a tre- 
mendous factor in determining the survival of types, vastly 
more so then than now; but wherever an improvement in the 
character of reproductive organs increased the certainty with 
which any plant could perpetuate its race, that gain could often 
far outweigh the superior vegetative. luxuriance of all com- 
petitors. This second factor in the “survival of the fittest” 
hs We ey 
E STER 
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