8 ORGANIC EVOLUTION 



find the greatest difference in the number of blossoms in a 

 single head ; the number of clusters of blossoms on a single 



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plant will vary greatly; the number of seeds is very variable, 1 

 so, also, is the proportion of these that will mature ; the size, 

 shape, and weight of the seeds vary ; within the seeds is a 

 variable amount of nutriment, and careful chemical analysis 

 would show that this nutriment is not absolutely constant in 



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character; the relative proportions of the parts within the 

 seeds are by no means constant, for in some seeds the embryo 

 will be relatively larger and the nutrient materials fill a 

 smaller space, while in other seeds these relations will be 

 reversed ; in the minute embryo which each seed contains 

 the relative proportions between the several parts, the minia- 

 ture stem and leaf and bud, are subject to much variation ; 

 examine still more closely, and you will find that in the cells 

 of which any portion of this minute embryo is composed 

 there is no uniformity in shape, size, or structure. The 

 analysis can be carried to any extent, and still it will be found 

 that every part of the organism is variable, and that this vari- 

 ation is not confined to a particular direction. The flowers 

 of the arbutus, for example, vary, not in a single regard. 

 They vary in number, size, shape, number of petals, length of 

 petals, breadth of petals, thickness of petals, color of petals, 

 in the size of the nectaries upon the petals, in the abun- 

 dance of the nectar secreted, in its strength of fragrance, in 



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its quality of fragrance, etc. I have developed this point to 

 the extent perhaps of wearying the reader, for it has not 

 usually been sufficiently prominent in the minds of those 

 who are thinking of the processes of evolution, and much 

 confusion and false thinking can be avoided if we remember 



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1 In many localities the trailing arbutus rarely matures seed. 



