EVIDENCE FROM EXPERIMENT 167 



the species of plants which inhabit the earth to-day 

 have proceeded from the different plant-forms of 

 the earth's earlier epochs. Experimental investiga- 

 tion and observation upon heredity in existing or- 

 ganisms prove that the specific characters of plants 

 are changeable, that especially by hybridization and 

 mutation new species of plants may arise from those 

 already present. The comparative study of struc- 

 ture and course of development in plants justifies 

 us in concluding that the species of plants, under 

 the continually acting influence of the external 

 conditions of life, lose certain possibilities of develop- 

 ment and gain new possibilities and may thereby 

 undergo a genealogical development." 1 



I must again remind you that what we are en- 

 deavouring to prove is a great historical process, 

 which has gone on through vast and unnumbered 

 aeons of time, when no observer was present to 

 record the forward steps in the magnificent proces- 

 sion of life. The details of evolutionary change 

 must have been of an unimaginable complexity and, 

 of necessity, the evidence for that change must be 

 chiefly indirect and circumstantial, to appreciate 

 the full force of which requires a certain degree of 

 technical training. The Indian hunter swiftly fol- 

 lows a trail which is invisible to the white man's 

 eye, and the experienced detective finds clues where 

 the average man sees nothing of importance, so only 

 one who has gained some first-hand knowledge of 



1 Karl Giesenhagen, in Die AbstaHKOungslehre, p 320. 



