CHAP. II. 
POLLEN. 
181 
modified simple leaves, for they constantly appear at a later 
period than the petals, although they afterwards develope 
themselves more rapidly; they stand at first higher up upon 
the axis than the preceding circle of corollary leaves, and 
they alternate invariably with them. 
Such is the structure of the stamens in their perfect state. 
It often, however, happens that, owing to causes with which 
we are unacquainted, some of the stamens are developed 
imperfectly, without the anther and pollen. In such cases 
they are called sterile stamens [ parastemones Link), and are 
frequently only to be recognised by the position they bear 
with respect to the other parts of the flower. Botanists con- 
sider every appendage, or process, or organ, which forms part 
of the same series of organs as the true stamens, or which 
originates between them and the pistil, as stamens, or as be- 
longing to what Roper calls the andrceceum, namely, to the 
male system ; and every thing on the outside of the fertile 
stamens is in like manner often referred to modifications of 
petals, a remarkable instance of which is exhibited by Passiflora. 
There is however no certain rule by which it can be deter- 
mined whether such bodies belong to the stamens or petals. 
The appearances assumed by these sterile stamens are 
often exceedingly curious, and generally very unlike those of 
the fertile stamens ; thus in Ganna they are exactly like the 
petals ; in Hamamelis they are oblong fleshy bodies, alterna- 
ting with the fertile stamens ; in Pentapetes they are filiform, 
and placed between every three fertile stamens ; in Zingi- 
beraceae they are minute gland-like corpuscles, a very common 
form (Plate IV. fig. 10. c) ; in Brodima they are bifid 
petaloid scales ; and in Asclepiadaceae they undergo yet 
more remarkable transformations. Dunal calls these sterile 
stamens lepals (lepala) ; a term which has not yet been 
adopted. 
9. Of the Pollen. 
The pollen is the pulverulent substance which fills the 
cells of the anther. It consists of extremely minute grains, 
varying in size, and enclosing a fluid containing molecular 
matter. The pollen-grains are often called granules, 
N 3 
