um.] Variation after Birth. 19 



that the same kind of adaptations to conditions are proceeding 

 everywhere before our eyes. We cannot stroll afield without 

 seeing it. Dandelions in the hollows, on the hillocks, in the 

 roadside gravel, in the garden — they are all different dande- 

 lions, and we know that any one would have become the other 

 if it had grown where the other does. 



But aside from the differences arising directly from physical 

 conditions of soil and temperature and moisture, and the like, 

 there are differences in plants which are forced upon them by 

 the struggle for life. We are apt to think that, as plants grow 

 and crowd each other, the weaker ones die outright, because 

 they were endowed with — that is, born with— different capa- 

 bilities of withstanding the scuffle. As a matter of fact, how- 

 ever, the number of individuals in any area may remain the 

 same or even increase, whilst, at the same time, every one of 

 them is growing bigger. Early last summer I staked off an 

 area of twenty inches square in a rich and weedy bit of land. 

 When the first observations were made on the the 10th of July, 

 the little plat had a population of 82 plants belonging to 10 

 species. Each plant was ambitious to fill the entire space, and 

 yet it must compete with 81 other equally ambitious individ- 

 uals. Yet, a month later, the number of plants had increased 

 to 86, and late in September, when some of the plants had 

 completed their growth and had died, there was still a popula- 

 tion of 66. The censuses at the three dates were as follows : 



July lo. Aug. 13. Sept. 25. 

 Cr;)l. grass (Panicum sanguinale) . -- 2n 15 



Black Mr.liek (Modicum lupulina) • 16 17 15 



Pigweed (Cheuopo< 

 Shepherd's Purse 



What a happy family this was ! In all this jostle up to tl 

 middle of August, during which every plant had increased i 



