548 



PHANEROGAMS. 



which spring from the upper margin of the hollowed-out receptacle which constitutes 

 the inferior ovary \ 



The size and form of the stamens frequently varies within one and the same 

 flower; thus, for instance, in the Cruciferse there are two shorter and four longer 

 (tetradynamous), in the Labiatae two larger and two shorter (didynamous) stamens ; 

 in Cen/radem'a, as was shown in Fig. 364, A, B, they are not only of different size, 

 but are also differently segmented. A correct conception of the history of develop- 

 ment and a comparison of the relationships of number and position in nearly allied 

 plants enable one to apply the term stamen even to structures which have no anther 

 and therefore want the ordinary physiological character of stamens. Thus, for 

 example, in Geranium there are two whorls of fertile stamens, while in the nearly 

 related genus Erodium those of one whorl are without anthers. Such sterile stamens 

 or Staminodes generally undergo further metamorphosis, by which they become unlike 

 the fertile ones and not unfrequently petaloid, as the innermost staminal leaves of 

 Aquilegia ; or assume very peculiar forms, as in Cypripedium (Fig. 372, s). In 



Fia 372.— Flower of Cypripedium Calceoliis after removal of the perianth. 



some Gesneraceae a glandular structure or nectary is found in place of the poste- 

 rior stamen (compare the drawing of Columnea, Fig. 416). Metamorphoses of 

 this kind may be considered as the first steps to a condition of abortion, the final 

 stage of which is the production of a vacancy at the spot where the stamen should 

 be, as in the Labiatas, an order closely allied to the Gesneraceae, where, in the place 

 of this staliiinode there is no structure whatever ; instead of the five stamens to which 

 the plan of construction of the flower points, there are only four, even the rudiment 

 of the fifth, the posterior one, being suppressed, as is seen in Fig. 373 2. Phenomena 

 of this kind altogether justify the hypothesis of abortion in those cases in which 

 the absent organ does not disappear in the course of development, but never comes 



. * Compare the account of the development and significance of the flowers of Orchidese in the 

 sequel. 



^ [Peyritsch however (Sitzungsb. der k. Akad. der Wissen. zu Wien, 1872) infers, from the 

 constant reversion to fours in the peloric flowers of Labiatce, and from other considerations, that the 

 original type of the flower is tetramerous.] 



