MOKPHOLOGY OF EEPRODUCTIVE ORGANS 147 



Fig. 277. 



of the structure of the flower, which is not uncommon, is seen 

 in cases where one leaf or more of either of the whorls has 

 assumed an abnormal appearance or structure. Thus in the 

 Aconite the petals are developed as two 

 long slender bodies with a dilated head, 

 which stand together under the arched 

 upper sepal (fig. 111). In the Hellebore 

 all the petals are represented by small 

 tubular bodies which are nectaries. In 

 some flowers again, particularly in culti- 

 vated forms, we meet with cases where 

 leaves of the andrcecium are developed as 

 petals. This is most generally found in 

 flowers which have typically many stamens, 

 e.g. Eoses, Buttercups, &c. We have as 

 a result so-called double floiuers. Occa- 

 sionally such a metamorphosis occurs in 

 wild flowers. 



Other forms of interference with normal 

 symmetry are due to modification of the 

 floral axis or thalamus. These will be 

 discussed later. Sometimes a flower which 

 is normally zygomorphic, from a single 

 petal being spurred, becomes regular, developing spurs to all 

 its petals. Such a flower is calleA pyloric. 



Fig. 277. A portion of the 

 flower of the Monkshood 

 (Aconitum}, with nu- 

 merous stamens below, 

 and two stalked some- 

 what liorn-shaped petals 

 above. 



The Parts of the Plowee. 



We must now examine the structure of the flower in greater 

 detail, dealing with the axis and its modifications, and with the 

 peculiarities of the separate floral whorls. 



(1) THE THALAMUS. 



The part of the flower-stalk or axis which is above the inser- 

 tion of the leaves of the calyx, and so is within the flower, has 

 been variously distinguished by botanists as the thalamus, re- 

 ceptacle, and torit-i. 



In the majority of plants it is a little flattened surface or 

 point, and accordingly presents nothing remarkable; but in 

 other plants it becomes much enlarged, and then assumes a, 

 variety of appearances, and modifies to a considerable extent 

 the form of the flower. In the species of Magnolia, Lirioden- 



u2 



