A manual of botany, anatomical and physiological : for the use of students / by Robert Brown.

Date:: 1874

Credit: A manual of botany, anatomical and physiological : for the use of students / by Robert Brown. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

542/656 page 520

$The further distinctions as regards developments we will reserve until we have occasion to speak of the process of germination ' (P- 527)- In the mean time, let us speak of the conditions of the 1 seed necessary to that process being performed ; and first, regard- j ing the GROWTH OF THE SEED. A seed attains its maximum size at an early stage of its growth. After this the tissues within the spermoderm solidify as the seed ripens, without, however, any further increase in size. There is even a decrease in the dimension of the seed as it ripens, by the ' contraction of the exterior, in this respect somewhat resembling the pericarp of some fruits. That the outside dimensions of the seed should be the parts which first arrive at maturity, it is neces- sary that the parts in the interior should have room to increase and solidify. After the secondary parts have thus attained their maxi- mum size, the embryo and the endosperm, which are the primary parts of the seed, become the chief centres of growth. The shape ' of the seed is greatly determined by the relative rapidity of the growth of parts. Ripetiing of Seeds.—Seeds are in their early state green—and 1 even the embryo is so also ; ^ but when they ripen, the exterior gets paler, whitish, white, or yellowish brown, owing to changes in the contents of the cells of the spermoderm. Some seeds are diver- sified, and often brilliantly variegatedly coloured, as we have a familiar example in the different varieties of kidney-beans. The bright glistening appearance of immature seeds is owing to the I presence of water in the spermoderm, and it decreases as the amount of water diminishes by drying, though some seeds are bright even when mature, owing to a peculiar condition of the epi- I dermal cells, or perhaps to the presence of some oily or waxy sub- stance. The decrease of the dimensions of the seed as it ripens is owing to the loss of water, on account of less and less sap arriving in the seed as it gets ripe, the result of which is the atrophy of the funic- ulus. The amount of water in dry seeds is about 4 per cent on right angles to it; but in the date-palm, where the slit of the cotyledon is a . vertical one situated near the base of the cotyledon, Professor A. Dickson has pointed out that there is presented an exception to the invariability of that rule (Nature, 1870, p. 38). The most recent research on the development of the j embryo in Monocotyledons and Dicotyledons is one published as these sheets ' are passing through the press—viz., by Johannes Hanstein (Botanische Ab- hand., Heft i.), which I have only seen in an abstract (by Dr M'Nab) in ^ Month. Journ. of Mic. Sc., 1873, p. 51. ^ ^ | 1 Some embryos, even in the ripe seed—e.g., mistletoe, Pistachia, some Cnici- \ ferae, &c.—remain quite green. ' , ]$

A manual of botany, anatomical and physiological : for the use of students / by Robert Brown.

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