attention must be given in order to keep it under conditions of temperature and moisture which favour regular and slow growth.

Observe from day to day the appearance of the growing corn and make a series of sketches showing the gradual development of the rootlets and the acrospire. Note also how the starchy part of the endosperm is modified in character as the growth of the embryo proceeds, and observe that this modification commences in the part of the endosperm which is nearest to the embryo, and gradually spreads towards the far end of the grain.

At intervals during the germination of the barley make longitudinal sections of a corn for microscopical examination. A freezing microtome should be employed, if possible, for making the sections. Prepare the sections for examination in the manner already described for preparing sections of barley (p. 14).1

Note that the first sign of the action of the growing embryo on the endosperm is the solution of the compressed layer of emptied cells adjacent to the scutellum (Fig. 13). This action is produced by the enzyme cytase which is secreted by the scutellum of the growing embryo. Cytase transforms the insoluble cellulose of the cell-walls into a soluble sugar.

1 See H. Brown and Morris, "Researches on the Germination of some of the Gramine" (The Visible Changes which occur in the Embryo and Endosperm during Germination), Journ. Chem. Soc., 1890, lvii., p. 466.

As the development of the embryo proceeds, note the disappearance of the cell-walls of the starch-containing cells of the endosperm which are nearest to the embryo, and the consequent liberation of the starch granules. Observe how the action spreads through the endosperm as the growth of the embryo proceeds. Note that it is this action which transforms the hard barley corn into the friable grain of malt.

Remove with the point of a needle a trace of the starch nearest to the scutellum of a partially grown barley corn, and examine it in water with a high-power lens. Note that many of the starch granules are "pitted "-i.e., show signs of being partially dissolved. This is due to the action of the enzyme diastase, secreted by the scutellum of the growing embryo. Diastase converts the insoluble starch granules into soluble sugar, and it is mainly by its action that the growing embryo obtains its necessary carbo-hydrate food from the endosperm.

Remove carefully the thick and thin skins from a well-grown barley corn, and note that the layer of aleurone cells can be readily detached from the rest of the endosperm. In a nongerminated barley corn this is not the case. The readiness with which the aleurone cells separate in a germinated corn is due to the fact that the aleurone cells, as well as the scutellum of the embryo,1 secrete cytase, and the action of this enzyme dissolves

1 See H. Brown and Escombe, "On the Depletion of the Endosperm of Hordeum vulgare during Germination," Proc. of Royal Soc., vol. lxiii., 1898.

the walls of the starch-containing cells adjacent to the aleurone layer, and so ruptures the connections between it and the starchcontaining cells of the endosperm. Hence the aleurone cells, as well as the cells of the epithelial layer of the scutellum, contribute towards the modification of the endosperm.

or

Demonstrate that the Embryo will Grow to a Limited Extent when Separated from its Endosperm and Supplied with Water only, and that it will Grow Freely under the Same Circumstances if it is Supplied with Suitable Food.'-Soak some barley corns (preferably six-rowed Chilian Smyrna) in water for twenty-four hours, and remove the embryos from about a dozen of the corns without injuring them. This may be easily done by turning back the skin of the corn at the germ end and lifting the exposed embryo with the point of a blunt knife.

Sterilise two small Petri dishes, each containing a flat piece of porous unglazed porcelain, about 2 square inches in area. Also prepare some sterilised water, and a sterilised 3 per cent. solution of canesugar. Pour sufficient sterilised water into one of the dishes to cover the bottom and thoroughly moisten the unglazed porcelain. Repeat this operation with the other dish, using the cane-sugar solution. Now place four or five of the excised

1 See H. Brown and Morris, "Researches on the Germination of some of the Graminea" (Culture of Embryos of Barley on Water), Journ. Chem. Soc., 1890, lvii., p. 482.

2 The embryos of these barleys are not so tender as those of two-rowed barleys.

barley embryos on the flat surface of each of the pieces of porcelain with the scutella of the embryos resting on the moistened surface of the porcelain. The embryos are then in a position to obtain the moisture they require in order to start them into growth. Place the covers on the dishes, and keep them in a moderately cool place. In about twentyfour hours signs of growth in the embryos will be noticed in both experiments. Protrusion of the roots is first observed, and shortly afterwards the plumules commence to elongate. During the first two or three days the growth of the embryos proceeds in both experiments at about the same rate, showing that water alone, as well as cane-sugar solution, stimulates germination. But by-and-bye the growth of the water-fed embryos ceases owing to lack of food, whilst the sugar-fed embryos continue to increase to a considerable size, and the young plants commence to develop chlorophyll.

If the cane-sugar solution contains suitable mineral nutriment and a little nitrate of potash, perfect plants can sometimes be reared.

When conducting the above experiments note that every precaution must be adopted to prevent the growth of moulds and bacteria, which readily attack the exposed embryos and check their development.

Demonstrate that the Embryo of the Barley Corn secretes Diastase during its Development.— Prepare 100 c.c. of a 1 per cent. solution of soluble

starch in water. Add to the solution when cold 7 grms. of gelatin, and heat gently in a water-bath until the gelatin is dissolved. Sterilise the solution in a steam steriliser, and when it is still hot pour it into a sterilised Petri dish, which is sufficiently deep to hold easily to an inch of the liquid. Place the cover on the dish and allow the gelatin solution to cool until it commences to show signs of setting. Now take several excised barley embryos which have been previously prepared, and place them on the surface of the setting jelly so that their scutella are in perfect contact with it.

FIG. 17.-Experiment Demonstrating the Secretion of Diastase by the Growing Embryo of a Barley Corn.

Put the covered dish in a cool place, and in three or four days the embryos will have developed considerably. Remove the cover from the dish, and with a knife make two long parallel cuts in the jelly, one on each side of an embryo almost touching it, and place the thin slice of jelly obtained in this manner on a white porcelain plate, and brush over it a solution of iodine in iodide of potassium. The iodine will stain most of the gelatin a deep blue colour, owing to the soluble starch present, but in the portion of the jelly situated immediately below the scutellum of the embryo a cup-shaped colourless part will be noticed. This is due to the