PARENT AND OFFSPRING 291 



oaks, etc. Even the descendants of a given set of parents 

 bear such resemblances that we readily recognize then- rela- 

 tionship. One family may have common characteristics that 

 separate them from other families of children, but the different 

 members of the family have distinctive characteristics. 



The apparently opposed statements which follow are there- 

 fore true : individuals of the same kind are never exactly alike, 

 but ordinarily these individuals have so many common char- 

 acteristics that their relationships are readily seen. 



318. The nature of variation. Individuals of the same kind 

 may differ from one another in almost every feature of which 

 they consist (fig. 133). If one selects the most widely different 

 grains of corn that he can find on a single ear, he will usually 

 be surprised at the variation. This is still better shown by 

 selecting grains from different ears grown in different places. 

 These are merely form and surface variations. Other kinds 

 of variations in corn will be discussed later. 



Equally great variations are found in other seeds. For in- 

 stance, the seeds of the common ragweed usually have distinct 

 spines upon the surface, but the number of spines varies. The 

 form and surface of 100 seeds were studied. The table below 

 shows the variation as found in the number of spines in these 

 100 seeds: 



Number of spines, 1, 2, 3, 4, 5, 6, 7, 8, 9 



Times occurring, 1, 3, 7, 9, 25, 37, 25, 12, 1 



The common bur marigold has conspicuous yellow ray 

 flowers. The number of these ray flowers varies, though this 

 variation is often unnoticed. A count of 315 heads of this 

 plant was made, and by means of this count the following 

 table was derived: 



Number of ray flowers, 3, 4, 5, 6, 7, 8, 9, 10, 11 



Number of times occurring, 2, 3, 8, 16, 52, 221, 9, 0, 1 



It is not only the form or the number of parts that varies, but 

 the chemical composition. In connection with attempts to grow 



