In conclusion, we must note one autumn flower of the woods which is exceedingly common--that of the Ivy (_Hedera Helix_), belonging to the order _Araliaceæ_. The Ivy is an evergreen climber, fixing itself by means of little rootlike suckers attached to the main stem and its branches, while the lower branches trail along the ground. The leaves are thick and glossy, usually of a deep green colour, but often beautifully variegated. Those attached to the trailing and climbing stems have three or five lobes, are always turned with one surface towards the light, and are so arranged as to obtain the maximum of light, the less exposed leaves below catching the rays which pass between the lobes of those which are more favourably situated. [Illustration: THE STRAWBERRY TREE IN FLOWER, WITH THE FRUITS (ALMOST RIPE) OF THE PREVIOUS YEAR.] The branches of the tree do not, as a rule, produce flowers as long as they are able to climb; but as soon as they reach the summit of the tree or wall to which they cling, or reach a situation where there is a sufficient abundance of light and air, they change their character in a remarkable way. They now become bushy, cease to produce suckers, and give rise to undivided leaves that turn in all directions for light and air. At the tip of each twig is formed a cluster of yellowish-green flowers, arranged in a short raceme or in an umbel. These flowers have an inconspicuous calyx which forms a border round the middle of the ovary, and five short petals. There are also five stamens, and united styles. The fruit is a smooth, black berry, containing from two to five seeds. XXIII PARASITIC PLANTS A number of plants extract more or less of the organic material they require from other plants, and thus save themselves the labour of building up this material themselves. These are termed parasites; but we must be careful to distinguish between them and certain other plants which, though apparently parasitic, are not really so. One plant may climb on another, perhaps even producing "rootlets" by which it clings to its living support, and yet it may not be a parasite in the proper sense of the term, for it may not absorb the slightest amount of nutritious matter except from the soil and the air. It is not at all uncommon for the Honeysuckle to twine its stems round the trunk and branches of a young tree, with the result that the tree becomes stunted, and assumes a starved appearance, especially in its lower parts; and yet the Honeysuckle is not a parasite. It has withdrawn nothing from the tree which supports it, but has coiled itself so tightly round it as to interfere with the circulation of its sap. The lower part of the tree is especially affected because the strangulating coils of the climber prevent the downward flow of the sap contained in the vessels of the bast or inner bark, and this is the sap which holds the constructive materials that have been built up in the leaves, under the influence of light.