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flatwormsThe flatworms, or Platyhelminthes, Plathelminthes, or platyhelminths (from the Greek πλατύ, platy, meaning "flat" and ἕλμινς (root: ἑλμινθ-), helminth-, meaning worm) are a phylum of relatively simple bilaterian, unsegmented, soft-bodied invertebrates. Unlike other bilaterians, they are acoelomates (having no body cavity), and have no specialized circulatory and respiratory organs, which restricts them to having flattened shapes that allow oxygen and nutrients to pass through their bodies by diffusion. The digestive cavity has only one opening for both the ingestion (intake of nutrients) and egestion (removal of undigested wastes); as a result, the food cannot be processed continuously.
In traditional zoology texts, Platyhelminthes are divided into Turbellaria, which are mostly nonparasitic animals such as planarians, and three entirely parasitic groups: Cestoda, Trematoda and Monogenea; however, since the turbellarians have since been proven not to be monophyletic, this classification is now deprecated. Free-living flatworms are mostly predators, and live in water or in shaded, humid terrestrial environments such as leaf litter. Cestodes (tapeworms) and trematodes (flukes) have complex life-cycles, with mature stages that live as parasites in the digestive systems of fish or land vertebrates, and intermediate stages that infest secondary hosts. The eggs of trematodes are excreted from their main hosts, whereas adult cestodes generate vast numbers of hermaphroditic, segment-like proglottids which detach when mature, are excreted, and then release eggs. Unlike the other parasitic groups, the monogeneans are external parasites infesting aquatic animals, and their larvae metamorphose into the adult form after attaching to a suitable host.
Because they do not have internal body cavities, Platyhelminthes were regarded as a primitive stage in the evolution of bilaterians (animals with bilateral symmetry and hence with distinct front and rear ends). However, analyses since the mid-1980s have separated out one subgroup, the Acoelomorpha, as basal bilaterians - closer to the original bilaterians than to any other modern groups. The remaining Platyhelminthes form a monophyletic group - one that contains all and only descendants of a common ancestor that is itself a member of the group. The redefined Platyhelminthes is part of the Lophotrochozoa, one of the three main groups of more complex bilaterians. These analyses had concluded the redefined Platyhelminthes, excluding Acoelomorpha, consists of two monophyletic subgroups, Catenulida and Rhabditophora, with Cestoda, Trematoda and Monogenea forming a monophyletic subgroup within one branch of the Rhabditophora. Hence, the traditional platyhelminth subgroup "Turbellaria" is now regarded as paraphyletic, since it excludes the wholly parasitic groups, although these are descended from one group of "turbellarians".
Over half of all known flatworm species are parasitic, and some do enormous harm to humans and their livestock. Schistosomiasis, caused by one genus of trematodes, is the second-most devastating of all human diseases caused by parasites, surpassed only by malaria. Neurocysticercosis, which arises when larvae of the pork tapeworm Taenia solium penetrate the central nervous system, is the major cause of acquired epilepsy worldwide. The threat of platyhelminth parasites to humans in developed countries is rising because of the popularity of raw or lightly cooked foods, and imports of food from high-risk areas. In less developed countries, people often cannot afford the fuel required to cook food thoroughly, and poorly designed water-supply and irrigation projects increase the dangers presented by poor sanitation and unhygienic farming.
Two planarian species have been used successfully in the Philippines, Indonesia, Hawaii, New Guinea, and Guam to control populations of the imported giant African snail Achatina fulica, which was displacing native snails. However, there is now concern that these planarians may themselves become a serious threat to native snails. In northwest Europe, there are concerns about the spread of the New Zealand planarian Arthurdendyus triangulatus, which preys on earthworms.
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budding plantWhat is Budding, Its Advantages and
Budding, oftenly called bud grafting, is an artificial method of asexual or vegetative propagation in plants. Like grafting, this method is employed to convert one plant (the rootstock) into another plant type with desirable characteristics. Similarly, the resulting plants in general have shortened stature and maturity as compared to plants propagated from seed.
This method of plant propagation has the advantage of producing numerous clones from a single piece of stem or twig, each node being a potential source of one-budded scion. But in grafting, this same piece of stem may account for only a single scion.
It is therefore advantageous where there is limited source of plant cuttings or scions for grafting. Likewise, the necessity of transporting bulky scions is eliminated. However, the clones produced take longer time to develop into the right sizes for outplanting than grafted seedlings.
Various techniques are used, mostly applicable to young plants in active growth with stems in which the bark is easily separable from the wood. Basically, the procedure in budding consists of the following steps:
1. Preparation of the rootstock. Rootstocks about the size of an ordinary pencil (~0.8 cm) and up to ~1.5 cm in diameter are commonly used but there are no hard rules. Chip budding is applied in citrus ~1/2 cm in diameter while other methods can apply to rootstocks up to ~2.5 cm (1 in) or even thicker. Potted seedlings are widely used but, similar to grafting, established trees may be top-budded. The specific techniques used in preparing the portion of the stem where union is intended vary;
2. Preparation of the bark to be joined to the rootstock. This consists of a prominent axillary bud (a plant organ which serves as growing point) on a section of bark, with or without a small piece of wood attached. This piece of bark is often termed as either a bud patch, chip, or shield piece. They are also referred to as single-bud scions.
Budsticks, small stems or twigs having multiple number of nodes from which the bud-containing barks are to be prepared, are obtained from well selected vigorous, disease-free mother plants having desirable characteristics and immediately defoliated. As in rootstocks, the preparation techniques are numerous;
3. Insertion of the prepared bark. The prepared patch, chip or shield piece is inserted into the part of the stem of the rootstock to replace the piece of bark that is removed or where cuts are made to allow union. Correct polarity should be observed, that is, the patch of bark is oriented upward.
4. Tying or wrapping. The stem-bud union is tied or wrapped to hold the components firmly together but generally leaving the growing point exposed. If also wrapped, it must be opened about 15 days later or at the time when the rootstock is cut back. There are various ready-to-use wrapping materials. A specialized wrapping strip made of rubber expands as the rootstock grows and naturally deteriorates after several weeks. But for practical usage, a thin, transparent polypropylene (PP) plastic bag can be cut into strips about 2-3 cm wide. These plastic strips have to be elastic and do not easily break when stretched;
5. Cut back of the rootstock. The rootstock must be decapitated, preferably with the use of a pruning shear, at the part of the stem immediately above the union to eliminate apical dominance. As a result, a new shoot will emerge from the growing point on the inserted bark which will then acquire apical dominance.
Cut back is done when it becomes certain that there is union which may take 15 days or more. The inserted patch of bark will remain green or otherwise brownish depending on the natural color of the budstick. If union is not successful, it will turn black and rot; and
6. Care of clones. This involves activities that are normally performed to hasten rapid growth of nursery plants and trees. It also includes debudding and desuckering, the removal of offshoots that may emerge from the stem below the union. These are done to ensure that the propagated plants will exhibit only the characters of the mother plant. Likewise, wrapping materials that take time to deteriorate, like PP plastic strips, must be removed at the earliest time possible to prevent strangling effect.
(Ben G. Bareja. November 2011)
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