The fallen petioles of our native ash-tree were next observed, and the rule with most objects, viz., that a large majority are dragged into the burrows by the more pointed end, had not here been followed; and this fact much surprised me at first.These petioles vary in length from 5 to 8.5 inches; they are thick and fleshy towards the base, whence they taper gently towards the apex, which is a little enlarged and truncated where the terminal leaflet had been originally attached.Under some ash-trees growing in a grass- field, 229 petioles were pulled out of worm burrows early in January, and of these 51.5 per cent.had been drawn in by the base,and 48.5 per cent.by the apex.This anomaly was however readily explained as soon as the thick basal part was examined; for in 78 out of 103 petioles, this part had been gnawed by worms, just above the horse- shoe shaped articulation.In most cases there could be no mistake about the gnawing; for ungnawed petioles which were examined after being exposed to the weather for eight additional weeks had not become more disintegrated or decayed near the base than elsewhere.It is thus evident that the thick basal end of the petiole is drawn in not solely for the sake of plugging up the mouths of the burrows, but as food.Even the narrow truncated tips of some few petioles had been gnawed; and this was the case in 6 out of 37 which were examined for this purpose.Worms, after having drawn in and gnawed the basal end, often push the petioles out of their burrows; and then drag in fresh ones, either by the base for food, or by the apex for plugging up the mouth more effectually.Thus, out of 37 petioles inserted by their tips, 5 had been previously drawn in by the base, for this part had been gnawed.Again, I collected a handful of petioles lying loose on the ground close to some plugged-up burrows, where the surface was thickly strewed with other petioles which apparently had never been touched by worms; and 14 out of 47 (i.e.nearly one-third), after having had their bases gnawed had been pushed out of the burrows and were now lying on the ground.From these several facts we may conclude that worms draw in some petioles of the ash by the base to serve as food, and others by the tip to plug up the mouths of their burrows in the most efficient manner.
The petioles of Robinia pseudo-acacia vary from 4 or 5 to nearly 12 inches in length; they are thick close to the base before the softer parts have rotted off, and taper much towards the upper end.They are so flexible that I have seen some few doubled up and thus drawn into the burrows of worms.Unfortunately these petioles were not examined until February, by which time the softer parts had completely rotted off, so that it was impossible to ascertain whether worms had gnawed the bases, though this is in itself probable.Out of 121 petioles extracted from burrows early in February, 68 were imbedded by the base, and 53 by the apex.On February 5 all the petioles which had been drawn into theburrows beneath a Robinia, were pulled up; and after an interval of eleven days, 35 petioles had been again dragged in, 19 by the base, and 16 by the apex.Taking these two lots together, 56 per cent.were drawn in by the base, and 44 per cent.by the apex.As all the softer parts had long ago rotted off, we may feel sure, especially in the latter case, that none had been drawn in as food.At this season, therefore, worms drag these petioles into their burrows indifferently by either end, a slight preference being given to the base.This latter fact may be accounted for by the difficulty of plugging up a burrow with objects so extremely thin as are the upper ends.In support of this view, it may be stated that out of the 16 petioles which had been drawn in by their upper ends, the more attenuated terminal portion of 7 had been previously broken off by some accident.
Triangles of paper.--Elongated triangles were cut out of moderately stiff writing-paper, which was rubbed with raw fat on both sides, so as to prevent their becoming excessively limp when exposed at night to rain and dew.The sides of all the triangles were three inches in length, with the bases of 120 one inch, and of the other 183 half an inch in length.These latter triangles were very narrow or much acuminated. As a check on the observations presently to be given, similar triangles in a damp state were seized by a very narrow pair of pincers at different points and at all inclinations with reference to the margins, and were then drawn into a short tube of the diameter of a worm-burrow.If seized by the apex, the triangle was drawn straight into the tube, with its margins infolded; if seized at some little distance from the apex, for instance at half an inch, this much was doubled back within the tube.So it was with the base and basal angles, though in this case the triangles offered, as might have been expected, much more resistance to being drawn in.If seized near the middle the triangle was doubled up, with the apex and base left sticking out of the tube.As the sides of the triangles were three inches in length, the result of their being drawn into a tube or into a burrow in different ways, may be conveniently divided into three groups: those drawn in by the apex or within an inch of it; those drawn in by the base or within an inch of it; and those drawn in by any point in the middle inch.