Development of the Embryo
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چکیده
Until 1804, when Salisbury found that orchid seeds could germinate, the seeds were considered sterile. Much later, in 1889, Bernard's discovery of the special conditions necessary for their growth and development explained the lack of success in previous attempts to obtain plantules, and the success, although mediocre, when sowing of seed took place at the foot of the mother plant. Knowing the rudimentary state of minute orchid embryos, one can better understand that an exterior agent, usually a Rhizoctonia, can be useful in helping them through their first stages of development (Bernard, 1904). Orchid embryos, despite their rudimentary condition, present diverse pattems of development, the most apparent of which are concerned with the character of the suspensor; there are other basic patterns that are revealed in the course of the formation of the embryonic body. These characteristics have been used differently in the classification of orchid embryos. This will be discussed in the first part of this chapter, to which will be added our knowledge of other phenomena concerning the embryo, in particular polyembryonic and apomictic seed formation. The second part of this chapter is devoted to the development of the young embryo, a study necessary for understanding the evolution of the different zones of the embryonic mass. We will also examine the characteristics of the embryo whose morphology, biology, and development are specialized when compared to other plants. 3 /-y , I', 1 d T 1, ,)i
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