84 THE MICHIGAN ACADEMY OP SCIENCE. 



THE IMPORTANCE OF PLANT VARIATION AND ITS BEARING 

 UPON THE EVOLUTION OF SPECIES. 



F. A. LOEW. 



The fact that plants have a tendency to vary from their original type 

 is of great importance to the horticnitnralist and the botanist alike. 



It is generally known that the causes of plant variation are environ- 

 ment, bud variation, and crossing. 



By environment we mean condition of soil, climate and surroundings 

 relative to other plants. 



It has been observed by all that by growing a plant on very fertile 

 soil there will be produced many abnormal shapes or types of the fruit 

 or of the stalk; this is due to the great amount of growth force accumu- 

 lated within the plant, which often gives vent to its power by the for- 

 mation of abnormalities. 



This fact can be illustrated by observing a cornfield planted on very 

 fertile soil ; scattered stalks of corn may be seen towering high above 

 their comi)anions; fasciated ears are not uncommon; corn growing on 

 the tassel is a conunon occurrence. 



It is a well known fact that southern perennial species have been 

 brought to our northern climates and after a number of generations have 

 acquired all the characteristics of annuals. The change of climate seems 

 to overthrow the equilibrium of the plant which causes it to begin at 

 once to adapt itself to its new circumstances, this adaptation being neces- 

 sary for its perpetuation in the struggle for existence. An example of 

 this is our common potato, which formerly was a perennial, but on be- 

 ing brought north and grown in these colder climates it took on the 

 habit of ripening its stalks and tubers before the approach of winter; 

 this of course was assisted by selection on the part of the cultivator. 

 Manv other southern ])]ants have been so ameliorated that thev can 

 produce their seed in this climate, but their stalks do not die until 

 killed by the frost; although they are not truly annuals, yet they have 

 been greatly changed in tlieir period of production of seed; such are 

 the tomato, the red pepi)er, the castor-bean, etc. 



It has been said that the vegetation of Mt. Rainier whose flora, 8,000 

 feet above the sea level, makes its season's growth and produces seed in 

 one month, or six weeks time; while at the foot of the mountain the 

 same species of plants require three months to accomplish the same 

 result. This shows the great plasticity of plants and with what ease 

 they adapt themselves to their surroundings. 



When a jjlant is crowded by other plants it sets about adapting itself 

 to its crowded condition ; sometimes it dies in the attemi)t, but at other 

 times it is greatly changed in its habit and form. Thus the common rag- 

 weed when grown in good soil reaches a lieight of five to six feet with 

 both ]>istillate and staminate 'flowers, but when grown in a crowded con- 

 dition it produces its seed when less than a foot high, but in many cases 



