Dispersal of tree seeds by water, as in the case of certain water plants, occurs less frequently. Of the European trees the older is one whose seeds are dispersed by water as well as by the wind, and of the tropical species the coconut palm is a noteworthy example.
Simultaneously, however, there are great losses both of the seeds and the young plants. Large quantities of seeds are eaten by birds and animals and many fall in places unsuitable for growth where they either do not germinate at all or die shortly after germinating, having used up the store of food in the seed. Similarly, many young trees are destroyed in their first years by drought, frost, invading grass or other plants, or by animals that feed on them. Of the huge crop of seeds, all that usually remains within a few years is less than one per cent per hectare.
In most conifers the seeds are contained in a cone consisting of carpels attached to a central axis that becomes woody.
A third group is formed by seeds which are themselves food for birds and mammals (oak, beech, walnut) and even though most are eaten, some are way. One would think that seed dispersal by animals is less effect ive than by wind, but the history of tree migration in the wake if retreating ice sheet in the period following the Ice Age gives evidence to the contrary.
True fruits are further divided into dry and fleshy fruits. Dry fruits with a dry and hard outer wall are Samara - usually a winged, one-seeded fruit with thin, membranous to leathery coat (birch, elm, ash). Dry fruits includes nut - a one-seeded fruit with hard, woody wall not connected with the seed (hazel, lime, hornbeam); Legume - usually the product of two carpels splitting along two lines of suture when ripe and containing several seeds; characteristic of most members of the family Leguminosae; Capsule - a single or several valved fruit splitting in various ways when ripe and containing several seeds (poplar, willow, chestnut).
On the other hand, shade-tolerant trees such as beech and oak, whose offspring can thrive in shade and appreciate the protection of the surrounding forest in their first years, have heavier seeds that do not fall far.
Simultaneously, however, there are great losses both of the seeds and the young plants. Large quantities of seeds are eaten by birds and animals and many fall in places unsuitable for growth where they either do not germinate at all or die shortly after germinating, having used up the store of food in the seed. Similarly, many young trees are destroyed in their first years by drought, frost, invading grass or other plants, or by animals that feed on them. Of the huge crop of seeds, all that usually remains within a few years is less than one per cent per hectare.
In most conifers the seeds are contained in a cone consisting of carpels attached to a central axis that becomes woody.
A third group is formed by seeds which are themselves food for birds and mammals (oak, beech, walnut) and even though most are eaten, some are way. One would think that seed dispersal by animals is less effect ive than by wind, but the history of tree migration in the wake if retreating ice sheet in the period following the Ice Age gives evidence to the contrary.
True fruits are further divided into dry and fleshy fruits. Dry fruits with a dry and hard outer wall are Samara - usually a winged, one-seeded fruit with thin, membranous to leathery coat (birch, elm, ash). Dry fruits includes nut - a one-seeded fruit with hard, woody wall not connected with the seed (hazel, lime, hornbeam); Legume - usually the product of two carpels splitting along two lines of suture when ripe and containing several seeds; characteristic of most members of the family Leguminosae; Capsule - a single or several valved fruit splitting in various ways when ripe and containing several seeds (poplar, willow, chestnut).
On the other hand, shade-tolerant trees such as beech and oak, whose offspring can thrive in shade and appreciate the protection of the surrounding forest in their first years, have heavier seeds that do not fall far.
About the Author:
Garden planning design should be fairly detailed and specific and include an indication of the type of planting envisaged in the different garden beds.
Tidak ada komentar:
Posting Komentar