292 PROCEEDINGS OF THE ACADEMY OF [1893. 



that my opportunities for further observations on this plant were 

 so limited. It affords a promising field for others more fortunate. 



The Relation between Rhythmic Growth and Variety 



in Citrus Fruits. 



The recognition that growth is rhythmic, and not one continuous 

 act, affords a ready explanation of many phenomena otherwise 

 inexplicable ; and this is well illustrated by a comparison of vari- 

 ous forms of fruit in the orange and other varieties of the citrus 

 tribe. 



Occasionally an orange may be found wholly formed inside of 

 another orange, and more frequently an orange will be found pro- 

 jecting from the apex of another — that is, but partially enclosed — 

 while in another which has been propagated as a distinct variety 

 and called the Navel orange, a very small attempt to form another 

 fruit at the apex is generally seen giving the navel or umbilical 

 appearance from which the variety derives its name. 



The morphological unity of the foliaceous and floral parts of a 

 plant being conceded, we conceive of the axis as being arrested in 

 its longitudinal development when a flower is being formed. In 

 most oranges we find the axis still extending a considerable distance 

 into the fruit, but varying very much in consistency in different 

 varieties. Sometimes it is quite woody, in others it is found cellu- 

 lar and so soft that it can be compressed between finger and thumb ; 

 while in some — notably in a variety known as the Tangerine — there is 

 rarely but a few lines of axis, usually no axis at all. 



The rhythmic waves of growth are not all of equal measure. 

 As in jumping a ditch, a boy may now rest exactly where he lands, 

 and now have to continue several paces before final rest, so does the 

 wave force in growth vary in intensity. In the process of the 

 metamorphosis of a branch with its various nodes into a flower and 

 finally a fruit, the expenditure of force in the arrestation of axial 

 growth and the development of the appendages to petals, stamens 

 and carpels is exactly meted to the results — now it is short of the 

 mark, and the axis starts under another rhythmic movement 

 the next time to be arrested for good and all. 



It is this succession of growth rhythms that produces the double 

 fruit oranges, but the phenomenon is not confined to the citrus 

 tribe. In the formation of cones in the coniferous family the 

 branch in its axial growth is usually wholly suppressed ; but occa- 



