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PRINCIPLES OF PLANT-TERATOLOGY. 



fused in pairs to form a 2-merous corolla, the resulting 

 two petals being in the antero-posterior position, and 

 thus alternating with the two stamens of the outer 

 whorl. 



In Veronica Buxbaumii Camus found a flower with 

 two petals* only, these being in the antero-posterior 

 position ; this represents a further advance in the 

 evolution of the flower towards the 2-merous con- 

 dition. Camus says that the Caucasian V. Crista-Galli 

 has two sepals only as a normal feature. In the 

 majority of species the corolla is normally 4-merous, 

 due to fusion of the two posterior petals ; and a point 

 to be noted is that the resultant structure is by no 

 means always larger than the lateral petals, but 

 sometimes equal in size to, and even smaller than, 

 these, f 



Magnus describes the various forms assumed by the 

 very small, more or less vestigial flowers which occur, 

 as a rule, close below the large terminal peloric flower 

 in the foxglove {Digitalis purpurea) ; their exceedingly 

 reduced structure and size is due to the absorption 

 into the terminal flower of the greater part of the 

 food material. Of these the form which appropriately 

 comes under this heading need only be cited. 



In flowers consisting of a corolla only, which was 

 monomerous (consisting of a single petal), was in the 

 form of a closed tube, and either regular or irregular, 

 one cannot say what the precise origin of this single 

 petal was. Then there is the case observed by Magnus 



* It is quite correct, in spite of what some systematists inform the wiiter, 

 to speak of petals in these cases of gnmopetalous corollas ; for whatever 

 happens, either in the way of fusion or division, to the corolla-lobes must be 

 regarded as happening to the corresponding extension of them below in the 

 tube. 



f A well-known systematist informs the writer that a petaloid structure 

 which is known to result from the fusion of two or more petals must always 

 be regarded as a compound structure, as in the " dps " of Labiatse, and if 

 the posterior petal of Veronica originates from a fusion of two petals, it must 

 be regarded as two petals, not one. To this the writer must entirely demur ; 

 where the union is so intimate that all trace of the originally separate petals 

 has been lost, the organ may be regarded as a single petal ; still more is this 

 the case where, as in some species of Veronica, the supposed compound petal 

 is the same size as, or even smaller than, the others composing the whorl. 



