LUTHER BURBANK 



individual plant of the old variety by growing it 

 under hothouse conditions. 



Incidentally, the fact that the old rhubarb to be 

 forced successfully in the greenhouse must be 

 frozen furnishes another interesting illustration of 

 the value of a period of absolute rest or dormancy 

 for a plant, and will suggest analogies with other 

 cases of the same kind elsewhere cited. Seem- 

 ingly the tissues of the plant root, having been 

 frozen even for a brief period, have no way of 

 estimating the length of time during which they 

 have remained dormant, and thus are ready to 

 respond to the climatic conditions about them 

 \vhen thawed out. So, finding themselves in the 

 atmosphere of the springtime, they begin their reg- 

 ular springtime growth. 



In a sense, the artifice of the gardener may be 

 said to fool the tissues of the plant, and to cause 

 it to take on an altogether abnormal activity. 



But, as just stated, this result applies only to 

 individual plants, and no one thinks of develop- 

 ing a race of Winter Rhubarbs in this way. 

 MIXED HEREDITIES 



The habit of perpetual bearing, as manifested 

 by my perfected varieties of Winter Rhubarb, was 

 explained as a development based on the compar- 

 atively recent residence of the ancestors of the 

 plant in a tropical climate. The fluctuating tern- 



[218] 



