Page:Transactions of the Linnean Society of London, Volume 12.djvu/71

Rh and falls to the bottom of the tube, where it is either drowned, or attempts in vain to ascend against the points of the hairs. The fly seldom takes wing in its fall and escapes; but this sometimes happens, especially where the hood has been removed to assist observation. In a house much infested by flies, this entrapment goes on so rapidly that a tube is filled in a few hours, and it becomes necessary to add water, the natural quantity being insufficient to drown the imprisoned insects. The leaves of the S. adunca and S. rubra of Walter might well be employed as flycatchers; indeed I am credibly informed they are in some neighbourhoods. The leaves of the flava, although they are very capacious, and often grow to the height of three feet or more, are never found to contain so many insects as the leaves of the species above mentioned. The spreading fauces and erect appendices of the leaves of this species render them (I suppose) less destructive.

The cause which attracts flies is evidently a sweet viscid substance, resembling honey, secreted by, or exuding from, the internal surface of the tube. On splitting a leaf it may readily be discovered in front, just below the margin, and in greatest quantity at the termination of the ala ventralis. From the margin, where it commences, it does not extend lower than one-fourth of an inch. During the vernal and summer months it is very perceptible to the eye and touch; and although it may be sometimes not discoverable by either, yet the sensation of sweetness is readily perceived on applying the tongue to this portion of surface. In warm and dry weather it becomes inspissated, resembling a whitish membrane.

Rh