During cold and tempestuous weather the presence of leaves may be a danger to the plant rather than a help; and where seasonal variations are such that strongly contrasted periods of favourable and unfavourable weather occur, such as the summer and winter of our own climate, many plants have adopted the device of shedding all their leaves: this is especially characteristic of the largest plants (the trees), which would naturally suffer most from unfavourable weather. The fall of the leaf is accomplished by means of the formation of a transverse layer of corky tissue across the base of the leaf-stalk, combined with a weakening of the layer of cells immediately above. Prior to the perfecting of these arrangements for dropping the leaf, all the useful materials in it are withdrawn down the stem, so that only an empty skeleton is shed; the scar that remains is not an open wound, but is well protected by the corky layer before mentioned. Stipules and bracts need not delay us in this sketchy survey of plant organs. They are leaves, generally of rather small size, placed, the former one on either side of the point where a leaf-stalk emerges from the stem, the latter singly below a flower; they are present in some plants, absent from others. They function in the same way as ordinary leaves, and in the earlier stages of growth are of use protectively. Occasionally the stipules exceed or even replace the leaves, as in the native _Lathyrus Aphaca_, where the leaf is reduced to a tendril, and the pairs of broad “leaves” are really the stipules. The bracts, in their turn, sometimes take on the “advertisement” function of the petals, as we have already seen (p. 87) in the case of certain Euphorbias. The leaves of water plants offer several points of interest. Where they are entirely submerged, and, protected against the drying influence of wind and sun, they are of filmy texture. Broad blades are seldom met with, the leaves being usually either finely dissected or strap-shaped. The floating leaf, on the contrary, as already described in the Water Lily, is strongly built up, to withstand wave action and rain; it is usually broad and entire, which simplifies the [Illustration: FIG. 23.--SPRING SUCCESSION OF LEAVES OF MATURE PLANT OF ARROW-HEAD (SAGITTARIA SAGITTIFOLIA). 1/3.]