FERTILISATION OF VARIOUS FLOWERS BY INSECTS. 161 
explained, viz. the manifest connection which exists between the 
presence of nectaries and irregularity of the corolla. “ It is to 
be remarked,”* says A. de Jussieu, “that the development of a 
nectary on any particular part, stands frequently in intimate 
relationship with the irregularity of the flower, and seems to 
determine irregularity on that side where it is situated.” This 
intimate connection of two structural peculiarities becomes per- 
fectly intelligible if it be admitted, as urged above, that the two 
have one common object, viz. the promotion and utilisation of 
the visits of insects. 
I have already in two former numbers of this Keviewf given 
sundry illustrations of the preceding remarks. To those illus- 
trations I would now add some others. Combining these wflth 
the former, I shall, I think, have shown reasons for concluding 
that nectaries and irregularity have for their final cause the 
promotion of intercrossing, and that the same purpose is often 
subserved by other structural peculiarities which might at first 
seem matters of indifference. Such, for instance, are the co- 
herence of the anthers (e.g. Gesenria , Composita) ; their irregu- 
larity in form (e.g. Erica , Salvia'), in number, length, or general 
arrangement ( Didynamia ); their mode of dehiscence (e.g. 
Vaccinium , Arbutus, &c.), its period (e.g. Digitalis), and the 
direction of their dehiscent surfaces (e.g. Thyme, &c.). Such 
also are the set of the flowers on the stem (e.g. Melampyrum 
and Pedicularis) ; their mode of inflorescence (capital) ; the 
distribution of their colouring ( Pelargonium ), and perhaps even 
the size of the calyx ( Pedicularis ). 
I have already pointed outj how in Thyme and Marjoram 
intercrossing is much facilitated by the close crowding together 
of the flowers, in some of which the stigmas, in others the 
anthers, are alone mature : because a bee, crawling over the 
flowery surface, must inevitably convey pollen from blossom to 
blossom. The still closer crowding of the capital and the umbel 
may perhaps have a similar result. If it be so, we are furnished 
with the raison d’etre of these modes of inflorescence. 
As far, at any rate, as regards the capital, facts, I think, justify 
this supposition. If we examine a flower-head in any of the 
thousand composites, we find as follows : Firstly, in each in- 
dividual hermaphrodite flower the pollen ripens and is exposed 
before the stigma is mature. Secondly, the different flowers in 
the same head do not expand simultaneously, but the expansion 
begins with those of the circumference and extends centripetal !y. 
There are thus collected together flowers in every stage. Some 
in the centre, not yet open : outside these a ring of others, in 
“Botanique,” ninth edition, p. 312. 
t See the July number of last year, and the January number of this 
year. % P* 53. 
VOL. X. — NO. XXXV. M 
