ANGIOSPERMS. 



549 



into existence at all, if the hypothesis of the suppression of the part is confirmed 

 by a comparison of the relationships of number and position in nearly-allied plants. 

 The hypothesis of an abortion of this kind was, however, for the first time placed 

 on a firm basis by the theory of descent. 



The number of stamens in a flower is only rarely so few as one or two ; like 

 the perianth-leaves they are usually numerous, and they are then arranged in the 

 form of rosettes, either spirally or in whorls. If the arrangement of the perianth- 

 leaves is spiral, that of the stamens is usually the same, and the number of the 

 latter is then very commonly large and indefinite, as in Nymphcea, Magnolia, Ranun- 

 culusy Helleborus, &c. ; but in this case they are sometimes also few in number and 

 definite. 



Much more often, however, the stamens are arranged in one or more whorls, 

 those in one whorl being then usually equal in number and alternate with those in 



Fig. 373.— Various stages of development of the flower of Lamitun album ; I, II, III very young buds 

 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; /K horizontal section of an older bud, s tube of the gamosepalous calyx, / that 

 of the gamopetalous corolla ; a anthers, n stigmas ; y upper lip of the corolla with the epipetalous stamens ; 

 yi entire mature flower seen from the side. 



the other whorls, and with the perianth-leaves [symmetrical flowers of English text- 

 books]. There are, however, numerous deviations from this rule [unsymmetrical 

 flowers of English text-books] occasioned frequently by the abortion of particular 

 members or of whole whorls, or by their multiplication, or by the superposition of 

 consecutive whorls; and not unfrequently in the place of a single stamen two or 

 even more will arise side by side {dedoubkment). These phenomena, which are 

 often difficult to make out, are nevertheless of great value in the determination of 

 natural affinities, and will be still further examined in the sequel. 



Development of the Pollen and of the Anther-waW^ . The description given in 

 this place will apply only to the ordinary cases in which the pollen is formed in 



^ Nageli, Zur Entwickelungsgeschichte des Pollens, Zurich, 1842, — Hoftneister, Neue Beitrage 

 zur Kenntniss der Embryobildung der Phanerogamen, II. Monocotyledonen. — Warming, UntefS, Ub, 

 pollenbildende Phyllome und Caulome, in Hanstein's Bot. Abhdl. Bd. II. 1873. — [Goebel, Beit. z. 

 Entwickgesch. d. Sporangien, Bot. Zeit. 1881.] 



