. Elementary botany : theoretical and practical. A text-book designed primarily for students of science classes connected with the science and art department of the committee of council on education . Botany. Fertilisation I2S the calyx to the ovary, or the epipetalous or gynandrous arrange- ment of stamens, would be due to adhesion. It will often give an idea of how the parts of a flower are arranged with regard to cohesion and adhesion to make a floral diagram of it. Figs. 238, 239, and 240 are examples of how this should be done. In fig. 238 we have in a Rose a poly- sepalous polypetalous a
. Elementary botany : theoretical and practical. A text-book designed primarily for students of science classes connected with the science and art department of the committee of council on education . Botany. Fertilisation I2S the calyx to the ovary, or the epipetalous or gynandrous arrange- ment of stamens, would be due to adhesion. It will often give an idea of how the parts of a flower are arranged with regard to cohesion and adhesion to make a floral diagram of it. Figs. 238, 239, and 240 are examples of how this should be done. In fig. 238 we have in a Rose a poly- sepalous polypetalous apocarpous regular flower, whilst in the Potato (fig. 239) we have a gamopetalous syncarpous flower. The diagrams show the different way that the petals and carpels are represented in the two cases. Fig. 240 shows an irregular flower, as seen in the Sweet-pea. Fertilisation.—In order that the ovary and ovules may properly perform their functions, it is necessary that they should be fertilised by the pollen. The pollen grains adhere to the stigma (fig. 241, b\ and being nourished by the viscid secretion present, a portion of the intine protrudes either through an opening already existing in the extine, or forcing its way through a part where the outer walls are thinner. The pro- longation thus formed is known as a pollen-tube (fig. 242). These tubes grow down the loose con- ducting tissue of the style and enter the ovary. The time necessary for this varies from a few hours to several weeks. In the Crocus it takes from twenty-four to seventy-two hours ; in the Arum over five days, and in the Orchids even some months. Just previous to this, or about the same time, a change has been going on in the embryo-sac of the ovule. Usually one or two cells are produced within the embryo-sac at the end away from the micropyle. These are. Fig. 241. — Longitudinal section through the uniovular ovary of Polygonum Convolvulus at the time of flowering: a, stigma; b, pollen grains; c, poUen-tub
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectbotany, bookyear1888
