CHAPTER XV.

DROSOPHYLLUM—­RORIDULA—­BYBLIS—­GLANDULAR HAIRS OF OTHER PLANTS—­ CONCLUDING REMARKS ON THE DROSERACEAE.

Drosophyllum—­Structure of leaves—­Nature of the secretion—­Manner of catching insects—­ Power of absorption—­Digestion of animal substances—­Summary on Drosophyllum—­Roridula- -Byblis—­Glandular hairs of other plants, their power of absorption—­Saxifraga—­Primula—­ Pelargonium—­Erica—­Mirabilis—­Nicotiana—­Summary on glandular hairs—­Concluding remarks on the Droseraceae.

Drosophyllum lusitanicum.—­This rare plant has been found only in Portugal, and, as I hear from Dr. Hooker, in Morocco.  I obtained living specimens through the great kindness of Mr. W.C.  Tait, and afterwards from Mr. G. Maw and Dr. Moore.  Mr. Tait informs me that it grows plentifully on the sides of dry hills near Oporto, and that vast numbers of flies adhere to the leaves.  This latter fact is well-known to the villagers, who call the plant the “fly-catcher, " and hang it up in their cottages for this purpose.  A plant in my hot-house caught so many insects during the early part of April, although the weather was cold and insects scarce, that it must have been in some manner strongly attractive to them.  On four leaves of a young and small plant, 8, 10, 14, and 16 minute insects, chiefly Diptera, were found in the autumn adhering to them.  I neglected to examine the roots, but I hear from Dr. Hooker that they are very small, as in the case of the previously mentioned members of the same family of the Droseraceae.

The leaves arise from an almost woody axis; they [page 333] are linear, much attenuated towards their tips, and several inches in length.  The upper surface is concave, the lower convex, with a narrow channel down the middle.  Both surfaces, with the exception of the channel, are covered with glands, supported on pedicels and arranged in irregular longitudinal rows.  These organs I shall call tentacles, from their close resemblance to those of Drosera, though they have no power of movement.  Those on the same leaf differ much in length.  The glands also differ in size, and are of a bright pink or of a purple colour; their upper surfaces are convex, and the lower flat or even concave, so that they resemble miniature mushrooms in appearance.  They are formed of two (as I believe) layers of delicate angular cells, enclosing eight or ten larger cells with thicker, zigzag walls.  Within these larger cells there are others marked by spiral lines, and apparently connected with the spiral vessels which run up the green multi-cellular pedicels.  The glands secrete large drops of viscid secretion.  Other glands, having the same general appearance, are found on the flower-peduncles and calyx.

Fig. 14. (Drosophyllum lusitanicum.) Part of leaf, enlarged seven times, showing lower surface.