20 The American Naturalist [January, 



bulk from two to twenty times, only the crab grass— apparently 

 the most tenacious of them all — had fallen off; and yet the 

 area seemed to be full in the beginning ! How then, if all 

 had grown bigger, could there have been an increase in num- 

 bers, or even a maintenance of the original population ? In 

 two ways : first, the plants were of widely different species of 

 unlike habits, so that one plant could grow in a place where 

 its neighbor could not. Whilst the pigweed was growing tall, 

 the medick was creeping beneath it. This is the law of diver- 

 gence of character, so well formulated by Darwin. It is a 

 principle of wide application in agriculture. The farmer 

 " seeds " his wheat-field to clover when it is so full of wheat 

 that no more wheat can grow there, he grows pumpkins in a 

 cornfield which is full of corn, and he grows docks and stick- 

 tights in the thickest orchards. Plants have no doubt adapted 

 themselves directly, in the battle of life, to each other's com- 

 pany. 



The second and chief reason for the maintenance of this 

 dense population, was the fact that each plant grew to a differ- 

 ent shape and stature, and each one acquired a different long- 

 evity ; that is, they had varied, because they had to vary in 

 order to live. So that, whilst all seemed to have an equal 

 chance early in July, there were in August two great branch- 

 ing red-roots, one lusty ragweed and 83 other plants of various 

 degrees of littleness. The third census, taken September 25th, 

 is very interesting, because it shows that some of the plants of 

 each of the dominant species had died or matured, whilst 

 others were still growing. That is, the plants which were 

 forced to remain small also matured early and thereby, by vir- 

 tue of their smallness, they had lessened, by several days, the 

 risk of living, and they had thus gained some advantage over 

 their larger and stronger companions, which were still in dan- 

 ger of being killed by frost or accident. When winter finally 

 set in, the little plat seemed to have been inhabited only by 

 three big red-roots and two small ones and by one ragweed. 

 The remains of these six plants stood stiff and assertive in the 

 winds ; but if one looked closer he saw the remains of mi 

 lesser plants, each "yielding seed after his kind," each one 



many 



