Abstract
THE parasite Loranthus Kraussianus grows on the coast here on the tree Chœtacme Meyeri, and as three of these trees grow within a short distance of my house, I have this season had a good opportunity of observing the rather curious mode of its fertilisation. In the flower bud the corolla segments adhere along their whole length, forming an upright cylinder, of about an inch long, of red and white, thus getting the not inappropriate colonial name of “lighted candles.” The flowers grow in close umbels, so close together as to give quite a reddishtinge to the host tree. After a little time five slits appear about half-way up the upright cylindrical corolla, and these slits are about one quarter the length of the cylinder. The anthers occupy almost the extreme tip of the cylinder, and are pressed against each other by the closed tube of the corolla (the cylinder aforesaid), the actual tip being occupied by the capitate stigma. If a needle be inserted into one of the slits of the corolla with a downward movement, as if to seek the nectar at the base, it causes the tube to split with some force, and at the same time the anthers are quickly and forcibly released from their pressure one against the other, and fly downwards violently, scattering practically all the pollen they contain by the one movement; and at the same time the stigma, from being upright, springs to an angle of, say, 40 degrees on one side quite clear of the now split corolla tube. I found by microscopic observations of a number of stigmas just at this stage, that only in a small proportion of cases (I only found one) did any of the triangular pollen actually reach the stigma by the act of explosion, although the style was fairly thickly peppered. These flowers are constantly being visited by large numbers of the commonest coast sunbird (Cinnyris olivaceous), a very active and hardworking, though not very brightly coloured, member of the sun-birds. A little quiet watching will show the birds at these flowers splitting open flower after flower, and getting head and bill covered with pollen in moving about, undoubtedly fertilising the capitate receptive stigmas (in the receptive stage protruding free from the corolla tube) of other and older flowers. After seeing them thus at work, the question arose whether without their aid the bursting of the flower happened. The negative evidence was that although I had observed for many hours, I never saw a simple flower voluntarily explode; but to check this, I put a net-bag over a small branch containing, say, 80 to 100 healthy flowers. I found that when thus protected hardly a single flower got to a further stage than having the splits on the corolla tube ready for the outside aid of the sunbird to enable them to perform the next function, viz. explosion. Actually none exploded, and, as a consequence, not a single flower within the bag set seed. They seem to be quite sterile without outside help, the anthers debisce, but at a level below the capitate stigma, and as the corolla tube is generally upright the pollen is lost even as a self-fertilising agent. After careful watching, I feel sure sunbirds are the only effeciive agents in the fertilisation of this plant. At first I never observed bees visiting it, and actually made a note to the effect that they did not do so; but at a later date they came in good numbers. They seemed simply to follow the birds, and take any nectar left by them in the exploded flowers, and very seldom, and then, I think, only by a happy chance themselves caused the explosion. I did not observe any other insect visitors, so that it would appear this plant is dependent on Cinnyris; and there is an element of irony in it, for from the berries of this plant the boys make bird-lime, and the energetic efforts of these lovely little birds are towards the perpetuation of the means by which they are often made captive. It would be interesting to know how far the different individuals of Loranthus on the one tree are in the position of independent individuals of terrestrial species (pollen from an independent individual being necessary for the most perfect results of cross-fertilisation), or whether the fact of having a common host approximates them in this respect to the position of one plant, and whether to get the best results of cross-fertilisation pollen should be brought not from flowers of a different individual on the same host, but from plants growing on a different tree altogether. To carry on the life-history of this plant, my friend Mr. Harry Millar, of Durban, informs me that the berries when ripe are taken by the little tinker bird (Bar-betula pusilla), who eats the covering of the berry, and rejects the seeds and viscid matter around them, and to clear away the latter bangs the berry with his bill against a tree, where the seeds adhere with the viscid substance and germinate. I may say that Mr. Millar states that in shooting these birds, as specimens, he often finds the head and bill covered with pollen. I am informed that another sunbird (Cinnyris Verreauxi) visits this plant, but as it is of the same habits as C. olivaceous, the results of its visits, as far as the plant is concerned, would be the same.
Article PDF
Rights and permissions
About this article
Cite this article
EVANS, M. The Fertilisation of “Loranthus Kraussianus” and “L. Dregei”. Nature 51, 235–236 (1895). https://doi.org/10.1038/051235a0
Issue Date:
DOI: https://doi.org/10.1038/051235a0