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CHAPTEE 11. 



THE PRINCIPLE OF NUMBER. 



Number — Genehal Observations. — The first principle of 

 Variation to be considered is that of the number of parts 

 composing the different whorls of flowers. There are good 

 reasons for considering that six whorls, consisting of five, 

 four, three, or two parts each, as the case may be, should be 

 regarded as the theoretically complete number of verticils 

 of any flower. 



Anatomical investigations prove that the rule is for the 

 pedicel to contain — at least, immediately below the flower, — 

 if the latter be pentamerous, ten more or less distinct fibro- 

 vascular cords, five of which belong to the sepals and five to 

 the petals; if it be hexamerous, there will be six cords, three 

 for each whorl of the perianth. Each of these cords can 

 give rise by branching, first, to a whorl of stamens and 

 subsequently to a whorl of carpels, furnishing at least two 

 marginal and one dorsal cord for each of the latter. 



In many flowers bnth whorls of stamens are present, and 

 the androecium is then isomerous with the entire perianth. 

 More often one whorl is arrested, and then it may be either 

 one ; but most usually it is the petaline. On the other 

 hand, the calycine may not be developed as in Primroses, 

 Rhamnus^ etc. 



The absence of the petaline stamens is possibly attribu- 



