468 FACTORS OF ORGANIC EVOLUTION. 



this conception let us read again Francis Parkman's picturesque 

 description of the forest of Maine in his Half Century of Conflict. 



"For untold ages Maine had been one uubrolien forest, and it was so 

 still. Only along the rocky seaboard, or on the lower waters of one or 

 two great rivers, a few rough settlements had gnawed slight indenta- 

 tions into this wilderness of woods, and a little farther inland some 

 dismal clearing around a blockhouse or stockade let in the sunlight to 

 a soil that had lain in shadow time out of mind. This waste of savage 

 vegetation survives, in some part, to this day, with tlie same prodigality 

 of vital force, the same struggle for existence and mutual havoc that 

 mark all organized beings, from men to mushrooms. Young seedlings 

 in millions spring every summer from the black mold, rich with the 

 decay of those that had preceded them, crowding, choking, and killing 

 each other, i)erishing by their very abundance; all but a scattered few, 

 stronger than the rest, or more fortunate in position, which survive by 

 blighting those about them. They in turn, as they grow, interlock their 

 boughs, and repeat in a season or two the same process of mutual suffo- 

 cation. The forest is full of lean saplings dead or dying with vainly 

 stretching toward the light. Not one infant tree in a thousand lives 

 to maturity; yet these survivors form an innumerable host, jiressed 

 together in struggling confusion, squeezed out of symmetry and robbed 

 of normal development, as men are said to be in the level sameness of 

 democratic society. Seen from above, their mingled tops spread in a 

 sea of verdure basking in light; seen from below, all is shadow, through 

 which spots of timid sunshine steal down among legions of dark, mossy 

 trunks, toadstools and rank ferns, protruding roots, matted bushes, 

 and rotten carcasses of fallen trees. A generation ago one might find 

 here and there the rugged trunk of some great pine lifting its verdant 

 S])ire above in the distinguished myriads of the forest. The woods of 

 Maine had their aristocracy; but the ax of the woodman has laid them 

 low, and these lords of the wilderness are seen no more." 



In such bold and generalized examples as this the student is able to 

 discern only the general fact of progressive divergency and general 

 adaptation to conditions, without being able to discover the particular 

 directive forces which have been at the bottom of the evolution. It is 

 only when one considers a specific example that he can arrive at any 

 just conclusions respecting initial causes of modification. Of adaptive 

 modifications, two general classes have been responsible for the ascent 

 of the vegetable kingdom, one a mere molding or shaping into the 

 passive physical environments, the other the direct result of stress or 

 strain imposed upon the organism by wind and water and by the neces- 

 sities of a radical change of habit from aquatic to terrestrial life, and 

 later on by the stimuli of insects upon the flowers. One of the very 

 best examples of the mere passive ascent is afforded by the evolution 

 of the root as a feeding organ; and a like example of development as 

 a result of strain is afforded by the evolution of the stem and vascular 

 or fibrous system. Our present flora, like our present fauna, is an 

 evolution from aquatic life. The first sessile or stationary plants were 

 undoubtedly stemless. As the waters increased in depth and plants 

 were driven farther and farther from their starting points by the 

 struggle for place and the disseminating influence of winds and waves, 



