50 
rOPULAR SCIENCE REVIEW. 
ones in their development ? It cannot, I think, be for any other 
reason than that they are in closer proximity; in fact, close 
against the stigma, and that there would be great risk of self- 
fertilisation were they not to discharge their pollen before the 
viscid surface was mature ; whereas the lower anthers lie at a 
distance, and are much less dangerous. Were this not the case, 
there is no reason why the upper should precede the lower. 
In fact, when a useful purpose can be served, we find the lower 
pair preceding the upper. This is the case with woundwort 
( Stachys ). Here the lower pair ripen first, shed their pollen, 
and then retire laterally, one to the right, the other to the left. 
This they do in order to make room for the style to bend for- 
wards, and come into proper position. 
In examining the successive blossoms of a spike of foxglove, 
another fact will be noticed, which, as well as the general didy- 
namous structure, testifies to the importance of a vertical ar- 
rangement of the anthers. Each of these has two large lobes, 
which in the immature blossoms are placed horizontally, so as 
to cover a considerable breadth of the corolla. Were they to 
ripen in this position, most of their pollen would be wasted, for 
it would adhere to the sides of the humble bee, in parts entirely 
out of reach of the centrally placed stigmas. To avoid this, the 
lobes, as they ripen, change their direction and become vertical, 
lying close to the median line. (These successive changes are 
shown in figs. 5, 6, 7.) Their range is thus made to coincide 
with that of the stigma ; that is to say, a bee entering a freshly 
opened flower will have its back daubed with pollen in the 
same median line as will come into contact with the stigma 
when it visits a more mature blossom. 
The imperative necessity of keeping the anthers in the same 
line with the stigma may perhaps explain the anomalous struc- 
ture of the stamens in Prunella. In this flower, curious but- 
tresses project from the outer side of the filaments against the 
inner surface of the wide hood. These serve, I imagine, to fix 
the anthers more securely in the median line and to prevent 
any lateral divergence. 
There remains yet another point of interest. Why are there 
only four stamens in these didynamous flowers, even when calyx 
and corolla have five divisions ? and why is the missing stamen 
invariably the posterior one ? The reason is obvious. This 
stamen, were it present, would occupy the position which is 
wanted for the style. It is necessary that this shall lie against 
the wall of the corolla, so as to leave a free passage for insects. 
It is necessary that it shall lie against the 'posterior wall and in 
the median line, or its range will not coincide with that of the 
anthers, and the stigma will not strike the part of the bee on 
uhich the pollen is smeared. In fact, there is no other position 
