Page:Illustrations of Indian Botany, Vol. 2.djvu/131

ILLUSTRATIONS OF INDIAN BOTANY.

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A curious and widely distributed order of parasitical plants, abounding in species but with very few genera, seven only being enumerated by Meisner, the latest writer to whom I can refer, for upwards of 400 species. DeCandolle refers about 330 species defined by him to 3 genera, but some of these are certainly imperfectly known and others may be repetitions, which the author had no opportunity of detecting by comparison of specimens : but to set against these many have since been discovered, which will probably suffice to maintain the numbers nearly as here stated. In their habits the order is most remarkable, being with a very few exceptions parasitic, growing upon, insinuating their roots into the substance, and drawing their nourishment from the juices of living plants, a property, known to be possessed by very few cotyledonous plants in the whole circle of the vegetable kingdom. To fit them for this mode of propagation, their seed are covered with a viscid glutinous substance, which adheres tenaceously to whatever it comes in contact with, and retains it there, until circumstances favourable for exciting vegetation occur, when it pushes forth its radicle, the extremity of which it curves towards its support, on reaching which it becomes enlarged and flattened having the appearance of a sucker. From this enlargement the fibrous roots emanate, spreading themselves on all sides between the wood and the bark. In course of time, as the branch thickens by subsequent depositions of wood, these roots become gradually embedded in its substance, not by their power of penetrating it, but simply by new deposits over them. Though the space I have to devote to the subject is now greatly reduced, I cannot deny myself the pleasure of enhancing the value of my work by introducing a rather long extract "on the mode of Paritism," from a very able paper by Mr. Wm. Griffith, lately published in the Linnean transactions " on the ovula of Loranthus and Viscum."

"The only species in which this has been studied in any detail is the Viscum album, and even here the statements are not altogether satisfactory. The latest account which I have seen is that of DeCandolle in his excellent Physiologii Vegetale, vol. ii. p. 790, and more fully in vol. iii. p. 1409, where the subject is treated in the usually luminous manner, so characteristic of this distinguished author.

"The mature seeds of all the species of Loranthus adhere strongly to the substance on which they are applied by means of the viscous matter. This viscum soon hardens, and then has the appearance of a transparent glue. The first changes take place in L. scwrula two or three days after application, and consist of a curvature of the extremity of the radicle towards the support; this extremity when it reaches this point becoming enlarged and flattened.

"It has now the appearance of a sucker, such as those, for instance, of the Cassytha filiformis. I am unable to state the precise manner in which the radicle penetrates the bark. The operation seems to require some time, and it is not until it is completed that the plumula begins to be developed. In those species the cotyledons of which are soldered together, the plumula passes out by one of the clefts; in the others by the fissure between these two bodies. The cotyledons in all the species I have examined remain inclosed in the albumen, which substance begins to disappear as soon as the plumula commences to be developed; the cotyledons undergoing a corresponding diminution in size. By the time that the young plant is furnished with a pair or two of leaves the attachment will be found considerably firm. If we cut away the portions of the support, and lay bare the included portion of the parasite, we find that the application takes place entirely between the lignious systems of both, the fibres of the sucker-like root of the parasite expanding on the wood of the support iu the form of a pate d'oie. There is, however, no interchange of structure between them; neither at this period is there any intermixture of lignious fibres. As soon as the young parasite has acquired the height of two or three inches, when an additional supply of nourishment is probably required, a lateral shoot is sent out, which is, especially towards the apex, of a green colour. This at one or two, and subsequently at various places, adheres to the support by means of sucker-like productions, which are precisely similar in structure and in mode of attachment to the original seminal one.

"As the parasite increases in size, these lateral shoots become frequently very numerous, and give origin, I believe, always from those parts immediately opposite to the sucker like adhesion likewise to stems and branches. During the same period the fibres of the suckers be-