Botany : specially written to meet the requirements of teachers' D, matriculation, public service entrance, intermediate and pharmacy A examinations

presence of a protein, but the endosperm, except on its extreme outer edge, remains unchanged. Oil, though present, is not abundant. The foregoing investigations show that the true difference between monocotyledonous and dicotyledonous seeds is, as the names would suggest, that in the embryo of the former there is only one cotyledon, while in that of the latter there are two. Moreover, endosperm, which is present in all monocotyledons, is found in but few dicotyledons.

The Coconut is well worth study. It is really the kernel of the fruit, and, like a plum stone, consists of the seed contained in a hard shell. The white material that lines the shell and is eaten, is the endosperm, and the dark coat that adheres to it when it is broken away from the shell is really the seed coat. The germ is less than half an inch long, and is situated immediately beneath one of the thee eyes, the substance of this eye being thin and soft, and on germination affording a means of exit for the plumule. In the hottest part of the summer, place a coconut in a box of sawdust and keep it in a warm place, watering it thoroughly from time to time with lukewarm water. At night, wrap the box in an old woollen rug. The seed will germinate and the plumule appear through the eye. Now break open the nut and note the huge sponge-like sucker that absorbs the milk and flesh to be conveyed in solution to the young seedling.

The Date stone is a seed in which the hard material is endosperm. The embryo plant lies at the back on the side opposite the groove a short distance below the middle. On cleaning a date seed a depression will be noted at the back, where by scraping with a knife, the embryo plant may be exposed. This lies in a small cavity, and the sprouting rootlet makes its way out through the thin covering at the depression. The whole embryo may be extracted by placing the edge of a pocket-knife in the groove, and giving the back of

the blade a sharp tap. The seed splits and sets free the embryo. It is difficult, even with a lens, to distinguish cotyledon, radicle, and plumule. Soak the split endosperm in weak iodine solution. The fact that there is no blue coloration shows that starch is absent. Now place on the split surface a drop of strong sulphuric acid and the blue colour which indicates the presence of cellulose immediately appears.

Speaking broadly, we have now arrived at the conclusion that the seed is really a young plant which, together with its store of nourishment, has been formed from the ovule of the flower while still attached to and forming part of the parent plant. At a certain stage, the development of the embryo plant ceases, and we say that the seed is ripe. All growth then stops, and the seed, becoming dry, goes into a resting condition. This temporary arrest of development is an obvious advantage. The seed can, to some extent, choose its own time for renewal of growth. If, in the autumn when most of the seeds fall from the parent plants, the embryo were still growing, it would mean that the young plant would have to establish itself under adverse conditions. Autumn, in many places is the driest season of the year, and the tiny seedling would thus have to contend with scarcity of water, and later on be overwhelmed by the frosts and snows of winter. Instead, the embryo remains dormant till the warm spring rains supply the conditions most favourable to its growth.

The Mangrove, which grows on the mud-flats of the tidal inlets of the Auckland Peninsula, is modified to suit its peculiar environment. If the seed were dropped into the mud in an absolutely dormant state it would probably be carried out to sea before it had a chance to germinate. To avoid this, most mangroves show no arrest in the development of the embryo, growth being continuous from ovule to fully established tree.

In some species, the young plant becomes over a foot in length before detaching itself from the parent tree. Still growing, it falls into the mud, and, in the space of a few hours, is permanently established. The species that grows round the shores of Auckland Peninsula is peculiar in the fact that the seed does not fall out of the seed case, since the whole fruit detaches itself from the tree at one time. The seed does not escape till it reaches the water, when, under favourable conditions, though no radicle is present, it puts forth several slender roots that anchor the seedling to the mud. In the proper season, mangrove fruits may be commonly seen washing about along the shores of Waitemata harbour. When the seed case is removed the two large fleshy cotyledons appear, and the fact that there is no radicle may be readily observed.

GERMINATION. Let us now study the circumstances under which the embryo or infant plant resumes its interrupted development: in other words, let us consider the conditions necessary to germination, as the awakening of the seed is termed.

Moisture. - Every gardener knows that moisture is essential to germination. Seeds may be kept for years in a dry bag or box and there will be no sign of awakening: but only let the bag become wet, and, other conditions being favourable, germination will at once begin. The seedsman stores his seeds in a dry place so that they shall not germinate.

Experiment 1. - Place various kinds of seeds in moist sawdust and others on a dry shelf. The latter will not germinate, but if the weather is not too cold the former will.

Warmth is necessary. Everyone has observed that, in the colder parts of New Zealand, where a piece of

land has been dug or ploughed in late autumn, weed seedlings do not appear in any quantity till the winter frosts are over. No farmer thinks of sowing turnips at midwinter, while the tender French bean should not be put into the soil till all risk of frost is over. There is a maximum temperature above which, and a minimum below which germination will not take place. There is, moreover, an optimum temperature at which it proceeds most vigorously. These temperatures vary for different plants. In most plants cultivated in temperate regions vital activity is suspended below 40º F., while the maximum temperature is, in most cases, about 115º F. The optimum is between 80º and 95º according to the plant, wheat being 84º and maize 93º.

Experiment 2.- This experiment, which should be made in the summer time, can be carried out only where a refrigerator is working in the neighourhood, and ice can, therefore, without difficulty, be obtained at a low cost. Place a block of ice, (about six-pennyworth will be enough) in a fair-sized box, pack it below and at the sides with moist sawdust, and lay upon it various kinds of seeds wrapped in a piece of damp cloth. Now cover the whole to the depth of several inches with more of the damp sawdust. The seeds are wrapped in cloth to prevent their being scattered as the ice melts. As required, renew the ice every few days for a fortnight. There will be no germination. This shows that seeds will not germinate at a temperature below freezing point. That the seeds are not killed is shown by the fact that they germinate when ice is no longer supplied. Experiments to discover the maximum, minimum, and optimum temperatures, by means of germination experiments carried out in chambers constantly kept at a certain temperature, would be far more instructive than the foregoing, but are obviously beyond the scope of an elementary course.

Oxygen.- Now make experiments to show whether air, or rather oxygen, is required.

Experiment 3.- Place bean and other seeds in a bottle of water which has been recently boiled for some time to expel air. See tha the water reaches right to the mouth of the bottle and then cork it.

GERMINATION - insert diagram -

tightly. As a control (i.e., standard of comparison) place seeds in unboiled water, and leaving the bottle uncorked, from time to time bubble air with a pair of bellows or a syringe into the water. In the first bottle there will be no sign of germination, while in the second the seeds will sprout a little, though, owing to the limited supply of air, germination will not be very vigorous. We thus see that air, or one or more of its constituents, is necessary to germination.

Experiment 4 (Figs. 22 24).- Obtain three U tubes, place in one end of each, on mosit cotton wool or rag,