30 Plant-Breeding 



bud-variety, just as truly as every seedling is a seed- 

 variety, since no seedling is ever like its parent, and 

 there should be no greater mystery connected with the 

 sports of buds than there is with the varieties from seeds, 

 for the causes that produce the one may be and probably 

 are equally competent to produce the other (Figs. 6, 7). 



Struggle for life a cause of variation. We have seen 

 that the world is full of plants. There is room for more 

 only as the present individuals die. Yet nearly every 

 species produces a great number of seeds, and makes a 

 most strenuous effort to multiply its kind. Any one 

 plant, if left to itself, is capable of covering the earth in 

 a comparatively short time. A fierce struggle for a chance 

 to live is therefore inevitable. This conflict is most 

 apparent to the general observer in the springtime, when 

 every "herb yielding seed after his kind, and the tree 

 yielding fruit, whose seed was in itself, after his kind," are 

 sending forth a host of sturdy offspring. The very land 

 seems to be pregnant with weeds and aspiring young 

 growths. But by midsummer the numbers may be 

 less. The weaker and less fortunate ones have perished, 

 and the victors have waxed stronger thereby. The 

 annual and half of the biennial species complete their 

 course upon the approach of winter, and the older peren- 

 nial herbs are becoming weak; so in the succeeding 

 springtime there is again a fierce combat for the vacant 

 places. 



One of the results of this conflict is the adjustment of 

 plants to each other. We have seen how the climbing 

 plant insinuates itself amongst the shrubberies and ties 

 them together in an impenetrable tangle in order that 



