310 CULTIVATED PLANTS AND THEIR ORIGIN 



hence all our varieties of apples, pears, strawberries, tulips, 

 narcissus and many other cultivated plants do not ' come true ' 

 from seed ; so far as their usefulness is concerned there is no 

 necessity for them to do so, for the single original sport, when 

 once obtained, may be propagated vegetatively by cuttings, 

 runners, grafts and bulbs. Of course, varieties whose peculiar 

 characters are not hereditary cannot be ' fixed ' at all. Varieties 

 which are the result of hybridisation often vary for many genera- 

 tions, and are generally difficult to fix. On this account when 

 fixation is being attempted the several generations raised for the 

 selective process should be protected or prevented as far as 

 possible from crossing with other varieties and with the untrue 

 seedlings. 



Self-fertilisation or in-breeding, when not carried to an extreme, 

 tends to fix the characters of new varieties. 



(fi) Seminal or seedling varieties. — As previously mentioned 

 no two seedling plants are exactly the same; even when they 

 are derived from seeds taken from the same pod they differ from 

 each other in one or more particulars. It may be that the 

 colour of the flowers is not exactly the same, or the form of the 

 leaf, the thickness of the root, or the size and habit of growth of 

 the stem may differ in different individuals. Where the variation 

 from the common type is obvious and distinct we have termed 

 the plant a ' seminal sport ' ; seedlings showing lesser deviations 

 which are scarcely noticeable may be named ' seminal varieties' 

 Between a ' seminal sport ' and a ' seminal variety ' there is no 

 essential difference ; it is a matter of degree of variation only. 



These very slight indefinable deviations from the common 

 type are of the utmost importance, for experience teaches that 

 almost any one of them may be vastly increased by selecting and 

 cultivating the plant in which the peculiarity is most marked 

 in each successive generation ; the development of the peculiarity 

 and its fixation go on simultaneously in such cases. 



For instance, if among a bed of plants whose flowers are 



