1.] PLASTICITY OF NEW TYPES. 49 



It should be said that there is apt to be a fallacy in ob - 

 servation in these instances, because the records which 

 are, to our vision, simultaneous in the rocks may have 

 extended over ages of time; but it is nevertheless true 

 that some important groups seem to have come in some- 

 what quickly with many or several species, and to have 

 passed out with exceeding slowness. 



To my mind, all this is but the normal result of the 

 divergence of character, or the survival of the unlike. 

 A new type finds places of least conflict, it spreads rap- 

 idly and widely, and thereby varies immensely. It is a 

 generalized type, and therefore adapts itself at once to 

 many and changing conditions. A virile plant is intro- 

 duced into a country in which the same or similar plants 

 are unknown, and immediately it finds its opportunity 

 and becomes a weed, by which we mean that it spreads 

 and thrives everywhere. Darwin and Gray long ago 

 elucidated this fact. The trilobites, spirifers, conifers, 

 ginkgos, were weed -types of their time, the same as 

 the composites are to-day. They were stronger than 

 their contemporaries, the same as our own weeds are 

 stronger than the cultivated plants with which they 

 grow. After a time, the new types outran their oppor- 

 tunity, the remorseless struggle for existence tightened 

 in upon them, the intermediate unlikenesses had been 

 blotted out, and finally only one or two types remained, 

 struggling on through the ages, but doomed to perish 

 with the continuing changes of the earth. They became 

 specialized and inelastic; and the highly specialized is 

 necessarily doomed to extinction. Such remnants of a 

 vanquished host remain to us in the equisetums and 

 tree-ferns, in our single liriodendron, the single ginkgo 

 and sassafras, and the depleted ranks of the conifers. 



4 SUR. 



