54 
POPULAR SCIENCE KEVIEW. 
the position which brings it into contact with the bee as it 
crawls over the surface; that of the protected lobe is such that 
it will strike the bee’s head as it sucks the nectar (fig. 8). 
In most thyme plants the flowers are hermaphrodite. The 
stamens project from the corolla when the flower first opens; 
but it is only at a later period, when the pollen is in great part 
shed, that the style lengthens, and the stigma in its turn pro- 
jects. This would seem to afford a tolerable security against 
self-fertilisation. Nature, however, seems bent on erecting a 
still stronger barrier, by entirely separating the two sexes. For 
a considerable proportion of thyme plants have flowers in which 
the stamens are abortive, and reduced to mere rudimentary 
points inside the tube, while the stigma projects when the 
flower first opens.* There are thus thyme plants which bear 
only female flowers. Whether there are also others which bear 
only male flowers, I cannot say. I have, however, never found 
such an one. All that I have been able to make out is that 
very frequently in the hermaphrodite flowers the stigma fails to 
arrive at maturity. It seems hardly too rash to foretell that in 
the course of time these hermaphrodite flowers will cease 
altogether to possess stigmas, and that thyme will be purely 
dioecious. 
Still more surely may it be foretold of another plant — the 
horsechestnut — that in time it will be purely monoecious. If 
one of its pyramidal flower spikes be examined, the greater 
number of the flowers will be found to have the following 
structure. A sweet fluid is secreted at the base of the corolla, 
and access is open to this just under the two upper petals, on 
each of which is a dab of bright colour, while the rest of the 
corolla is white. The stamens are so curved and the anthers so 
set that a bee cannot get at the nectary without smearing its 
under surface with pollen. In the midst of the stamens a 
small pistil will be seen, which never developes to maturity, so 
that these flowers are in fact male flowers. Some few flowers, 
on the other hand, will be found in the spike, and almost 
always in the lower part, in which the style and stigma are 
fully developed, and have just the same curved form and 
position as above belong to the stamens and anthers. In these 
pistillate flowers there are also stamens ; but these are not turned 
towards the entrance to the nectary. Their anthers, moreover, 
as a rule, fall off without dehiscing, although there is pollen to 
be found on section within their lobes. These lower flowers, 
then, are practically female flowers, and their stigmas will strike 
* The flowers in which the stamens are rudimentary have also a much 
shorter tube than have the ordinary ones, so short that the lower lip is in 
contact with and supported by the two anterior long teeth of the calyx. 
