insect, should not fall sideways or backwards. We know that the ball of viscid matter at the extremity of the pollinium rapidly becomes more and more viscid, and sets hard in a few minutes' time: therefore we can see that it would be an advantage to the plant if the moth were delayed in sucking the nectar, so as to give time for the viscid disc to become immoveably affixed. Assuredly moths would be delayed if they had to bore through several points of the inner membrane of the nectary, and to suck the nectar from the intercellular spaces. This explanation of the good thus gained in some degree corroborates the hypothesis that the nectaries of the above-named species of Orchis do not secrete nectar externally, but into internal cavities.
The following singular relation supports this view more strongly. I have found nectar within the nectaries of only five British species of Ophreae, namely, in Gymnadenia conopsea and albida, in Habenaria bifolia and chlorantha, and in Peristylus (or Habenaria) viridis. The first four of these species have the viscid surface of the discs of their pollinia, not enclosed within the pouch, but naked, which by itself shows that the viscid matter has a different chemical nature from that in the species of true Orchis, and does not rapidly set hard when exposed to the air. But to make sure of this I removed the pollinia from their anther-cells, so that the upper as well as the under surfaces of the viscid discs were freely exposed to the air; in Gymnadenia conopsea the disc remained sticky for two hours, and in Habenaria chlorantha for more than twenty-four hours. In Peristylus viridis the viscid disc is covered by a pouch-formed membrane, but this is so minute that botanists have overlooked it. I did not, when examining this species, see the importance of exactly ascertaining how rapidly the viscid matter set hard; but I copy from my notes the words written at the time: "Disc remains sticky for some time when removed from its little pouch."
Now the bearing of these facts is clear: if, as is certainly the case, the viscid matter of the discs of these five latter species is so viscid as to serve at once for the firm attachment of the pollinia to insects, and does not quickly become more and more viscid and set hard, there could be no use in moths being delayed in sucking the nectar by having to bore through the inner membrane of the nectaries at several points; and in these five species, and in these alone, we find copious nectar ready stored for their use in the open tubular nectaries. If this relation, on the one hand, between the viscid matter requiring some little time to set hard, and the nectar being so lodged that moths are delayed in getting it; and, on the other hand, between the viscid matter being at first as viscid as ever it will become, and the nectar lying all ready for rapid suction, be accidental, it is a fortunate accident for the plant. If not accidental, and I cannot believe it to be accidental, what a singular case of adaptation!
CHAPTER II.
Ophreæ continued—Fly and Spider Ophrys—Bee Ophrys, apparently adapted for perpetual self-fertilisation, but with paradoxical contrivances for intercrossing—The Frog Orchis; fertilisation effected by nectar secreted from two parts of the labellum—Gymnadenia conopsea—Greater and Lesser Butterfly Orchis; their differences and means of fertilisation—Summary on the powers of movement in the pollinia.
WE now come to those genera of Ophreae which chiefly differ from Orchis in having two separate pouch-formed rostellums,[1] instead of the two being confluent, as in Orchis.
- ↑ It is not correct to speak of two rostellums, but the inaccuraty may be forgiven from its convenience. The rostellum strictly is a single organ, formed from the modification of the dorsal stigma and pistil; so that in Ophrys the two pouches and the intermediate space together form the true rostellum. Again, in Orchis I have spoken of the pouch-formed organ as the rostellum, but strictly the rostellum includes the little crest or fold of membrane projecting between the bases of the anther-cells. This folded crest (sometimes converted into a solid ridge) corresponds with the smooth ridge lying between the two pouches in Ophrys, and owes its protuberant and folded condition in Orchis to the two pouches having been brought together and become confluent. This modification will be more fully explained in the seventh chapter.
