4.>u 



PHANEROGAMS. 



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

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

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

 in Centradenia, as was shown in Fig. 333, 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 



n •<■.*-=-. r 



Fig. 342.— Various stages of development of tlie flower of I.amiiim album; /, //, /// very young budb 

 seen from above ; in / the rudiments of the sepals s are formed, in // those of the petals/, in /// those of the 

 stamens st and of the carpels c; /A' horizontal section of an older bud, i- tube of the gamosepalous calyx, / that 

 of the gamopetalous corolla; a anthers, ii stigmas ; V upper lip of the corolla with the epipetalous stamens ; 

 l^I entire mature flower seen from the side. 



Aquilegia ; or assume very peculiar forms, as in Cypripedium (Fig. 341 s). In 

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

 rior stamen (compare the drawing of Columnea, Fig. 385). 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 Labiatae, an order closely allied to the Gesneraceae, where, in the place 

 of this staminode 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. 342 \ Phenomena 

 of this kind altogether justify the hypothesis of abortion in those cases also where 



* [Peyritsch however (Sitzungsb. der k. Akad. der Wissen. zu Wien, 1873) infers, from the 

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

 the original type of the flower is letramcrous. — Ed.] 



