plants-vr-tropical-01-yam - more tubers grow down into the...

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Vegetative reproduction (tropical) 1 Vegetative reproduction - some tropical examples Stem tubers - the yam The yam ( Dioscorea spp.) is considered to be a stem tuber; that is, an underground stem swollen with food. The shape and number of tubers produced by a plant varies according to the species of Dioscorea and the method of planting and propagation. For example, the Chinese yam, Dioscorea esculenta , forms a large number of small yams, Dioscorea alata forms only one or two. One of the commonest methods of propagation is to cut a large tuber into eight or more pieces, called setts and plant them under the soil. Although no buds are visible either on or below the corky outer layer of the tuber segment a bud soon develops in the cortex. It sprouts a shoot and roots using the store of food in the sett. By the time the food reserve in the sett is exhausted there is an extensive leafy shoot, called a vine, with many leaves making food by photosynthesis. Some of this food is sent down the stem to the junction of root and shoot and at this point, one or
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Unformatted text preview: more tubers grow down into the soil. The sugar sent down from the leaves is turned into starch and stored in the tubers which swell greatly in diameter as a result. In September or October when the rains stop, the vine dies away and the yams are harvested. Sometimes, before the end of the rainy season, a yam tuber is dug up carefully without damaging the shoot, and the bottom 90 percent of the tuber is cut off and eaten. The remaining top part of the tuber with the vine still attached is replanted and continues growth but in this case it produces several small "seed" yams which are used as setts in the next growing period. (a) Portion of tuber (sett) planted ( b) Rapid cell division in an area of cortex (c) An outgrowth develops forming a shoot and roots soil level vine cortex (d) The vine and roots grow using stored food from the sett © D.G. Mackean...
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This note was uploaded on 11/29/2011 for the course BIO 218 taught by Professor Young during the Fall '11 term at BYU.

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