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By W. B. Crow (Auth.)

ISBN-10: 1483200299

ISBN-13: 9781483200293

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26 FORM AND STRUCTURE CHAPTER VEGETATIVE VI REPRODUCTION Also termed schizogony or fissiparous reproduction, meaning reproduction by fission or splitting. In plants special reproductive organs or parts are developed which function sexually or asexually. The remaining parts of the plant, including in higher plants stems, leaves, and roots, not specialized for reproduction, are called vegetative. Nevertheless they can and do reproduce the organism by vegetative reproduction and this term is extended in animals to those cases where reproduction takes place without the help of special reproductive organs ; it must not be confused with asexual reproduction, which is dealt with in the next chapter.

Two kinds of sperms are formed, 50 per cent of them having X and 50 per cent Y. Zygotes which get X X grow into females, those with X Y into males. In butterflies, moths, caddis-flies, some reptiles, and all birds the female is heterozygous. Their sex chromosomes in t h a t sex are called W and Z. Occasionally the smaller of the sex chromosomes is absent. The heterozygous sex then gets the odd chromosome XO or WO. B 2* 42 FORM AND STRUCTURE ZOIDOGAMY IN PLANTS Is somewhat similar to oogamy in animals.

The third category possess s e x c h r o m o s o m e s . Of the homologous pairs of chromosomes which their somatic cells possess one pair in one sex are unequal (heterozygous). Usually it is the male. The two chromo­ somes are called X - and Y - c h r o m o s o m e s . The female possesses two sex chromosomes both of which are alike and resemble the first, or X-chromosome. Two kinds of sperms are formed, 50 per cent of them having X and 50 per cent Y. Zygotes which get X X grow into females, those with X Y into males.

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A Synopsis of Biology by W. B. Crow (Auth.)


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