FACTORS OF ORGANIC EVOLUTION. 471 



annuals, normally completing their entire growth before the approach 

 of frost. It is all the result of adaptation to climate, and essentially 

 the same phenomenon is the development of the annual and biennial 

 flora of the earth from the perennial. An interesting example of the 

 effect of climate upon the seasonal duration of plants is the indeter- 

 minate or prolonged growth of plants in England as compared with 

 the same plants in America. The cooler summer and very gradual 

 approach of winter in England develop a late and indefinite maturity 

 of the season's growth. When English plants are grown in America, 

 they usually grow until killed by fall frosts; but after a few genera- 

 tions of plants, they acquire the quick and decisive habit of ripening 

 which is so characteristic of our vegetation. I once made an extended 

 test of onions from English and American seeds (Bull. 31, Mich. Agric. 

 College), and was astonished to find that nearly all of the English 

 varieties continued to grow until frost and failed "to bottom," while 

 our domestic varieties ripened up in advance of freezing weather. This 

 was true even of the Yellow Danvers and Red Wethersfield, varieties 

 of American origin, and which could not have been grown very many 

 years in England. Every horticulturist of much experience must have 

 noticed similar unmistakable influences of climate upon the duration of 

 plants. 



A most interesting type of examples of the quick influence of cli- 

 mate upon plants — not only upon their duration, but upon habit and 

 structural characters — is that associated with the growing of "stock 

 seed" by seedsmen. Because of uncertainties of weather in the East- 

 ern States, it is now the practice to grow seeds of onions, lima beans, 

 and other plants in California or other warm regions ; but the plants so 

 readily acquire the habit of long-continuing growth as to be thereafter 

 grown with difficulty in the Northeastern States. It is, therefore, 

 necessary that the seedsman shall raise his stock seed every year in 

 his own geographical region, and this seed is each year sent to Cali- 

 fornia for the growing of the commercial seed crop. In other words, 

 the seed of California-grown onions is sold only for the purpose of 

 growing onion bulbs for market, and is not planted for the raising of a 

 successive crop of seed. This results in growing only a single genera- 

 tion of the crop in the warm country. Onion seed from stock which 

 has been grown in California for several years produces onions which 

 do not "bottom" well, much as I found to be the case with the English 

 onion seed. 



But many plants, in geologic time, could not thus shorten up their 

 life history to adjust themselves to the oncoming of the seasons. They 

 ceased their labors with the approach of the cold or the dry, tucked up 

 their tender tissues in buds and resigned themselves to the elements. 

 If a man could have stood among those giant mosses and fern forests 

 of the reeking Carboniferous time, and could have known of the refrig- 

 eration which the earth was to undergo, he would have exclaimed 



