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BOTANY OF THE LIVING PLANT 



corolla can be pulled away in one piece, though its margin clearly 

 shows five petaline lobes. Further, if the corolla of the Primrose be 

 opened out, five stamens will be seen attached to the inner surface of 

 its tube. So not only is there a cohesion of the five petals to form a 

 tubular corolla, but also an adhesion of the stamens to it. COHESION 

 of parts of the same category [such as petals with petals), and ADHESION 

 of parts of different category [such as stamens to petals), are common in 

 flowers, and may be held as secondary modifications of their free condition, 

 as seen in the primitive state. 



This view is borne out by the study of development. For where the parts 

 are fused in the mature state, they still originate as separate papillae of tissue 

 from the growing point of the flower, just as the foliage leaves usually do. 

 It is later that the growth extends from the individual bases of these papillae 

 into the region between them. Consequently when mature they appear as 

 though borne up on a common base. This is well shown in the flower of the 

 Compositae, in which there is cohesion of the petals to form the tube of the 

 corolla, and adhesion of the stamens to the inner surface of that tube. 

 Fig. 198, p. 273, (v) and (vi) show how that adhesion arises. In (v) the stamens 

 and petals are independently inserted on the hollowed receptacle ; but the line 

 where basal growth will take place is indicated. In (vi) the result is seen ; 

 for they are there borne up on a common base, which has been the result of 

 that growth. 



(iv) Pleiomery. By this is meant that the number of parts of one 

 category is greater than the fundamental number for the whole flower. 



It is most frequently seen in the androecium, so 

 that the stamens are in excess of the other parts. 

 It may be a question exactly how this comes 

 about in each individual example. Branching 

 or fission of originally single parts may account 

 for some cases ; interpolation of additional parts, 

 where there is room for them on the receptacle, 

 may explain others. The distinction between 

 these is not always clear ; it turns upon compari- 

 son, and the observation of details of development. 

 The essential feature is, however, that more parts 

 FlG ' I9 °' of one category are produced than the other whorls 



Group of three stamens . 



of vdiozia, taking the of the flower would give reason to expect. 



place of one stamen in the 

 normal Liliaceous flower. 

 (After Eichler.) Fission is most easily recognised where two or more 



stamens stand side by side in the place normally occu- 

 pied by one ; it then sometimes happens that they arise from a common 

 stalk. The case of Vellozia (Fig. 190) gives a good example. Interpolation 

 of extra parts may give very similar results. Sometimes it is individual 



