THE PATH OF EVOLUTION 



of many groups of them has far surpassed that of 

 the longest lived tree known to history. Their debris, 

 when washed down by rain from the rock above, has 

 formed a soil retentive of the germs of mosses and 

 other cryptogamia, they in their turn when dead 

 decaying. When the successive increments have thus 

 formed enough humus, mixed with the rootlets 

 (hyphen) of the lichens and minute fragments of 

 rock, disintegrated by the weather, they are able to 

 give shelter and nourishment to the seeds of the 

 higher plants. Grasses, weeds, bushes, and at last 

 trees spring up, and a forest comes into being. Such 

 has been the path of evolution of vegetable life in all 

 parts of the globe. It begins with the simplest life, 

 that of an organism without differentiation of parts 

 other than a simple cellule ; it gradually gives place 

 to organisms of more complex structure as the for- 

 mation of soil progresses and permits the acquisition 

 of a higher life. 



The family of Lichens owe their preservation, if 

 not their existence, to an anomaly of structure pecu- 

 liar to them. It has been stated that all of the fungi 

 are devoid of chlorophyll, that constituent of plant 

 life that alone is capable of decomposing carbon 

 dioxide, appropriating its carbon to form starch, cellu- 

 lose or sugar, and rejecting or exhaling again the oxy- 

 gen into the atmosphere. Plants without chlorophyll 



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