or veins, in the palea inferior, which is now seen in cross-section.

The two true skins, the pericarp and testa, are also very clearly shown in the transverse section. Note how they continue round the grain until they arrive at the ventral furrow where they appear to be merged together and lost in a conspicuous dark brown spot called the funicle. This spot represents the point where the ovule was originally attached to the ovary of the barley flower before it developed into a corn (see Fig. 4, p. 5).

Within the thin skins of the transverse section, the triple layer of aleurone cells already noticed in the longitudinal section will be again observed. Within these lie the thin-walled starch-containing cells, forming the greater bulk of the endosperm. In general arrangement these cells will now be seen to radiate from near the centre of the grain.

Cut a Transverse Section of one of the Green Corns which are usually abundant in Samples of Six-rowed Barley.-Dehydrate the section, mount it in clove oil or balsam, and examine it under the microscope. Observe that the contents of the aleurone cells are coloured blue. The colour of the aleurone cells seen through the yellow outer skin of the corn is the cause of the green appearance of the corn originally observed. A green colour is a natural characteristic of certain varieties of two-rowed and six-rowed barleys and is not an indication of unripeness.

The student, after working through the studies described above, which should have given him a

good general knowledge of the structure of the barley corn, must now proceed to study some special points in the anatomy of the corn.

Note the Position in which Starch Granules occur in the Endosperm of Barley.—Transfer a thin transverse section of barley to a very dilute solution of iodine in a watch-glass, and allow it to remain in the liquid until the section is stained a distinct blue colour. Mount the section in water on a glass slide, cover with a thin glass, and examine first with a low and afterwards with a high power. The position of the blue-stained starch granules is now distinctly seen. It will be noticed that the aleurone cells contain no starch granules, and that these occur only within the thin-walled cells which compose the larger part of the endosperm. In these cells the starch granules lie very closely packed together.

Show that the Starch-containing Cells contain Protoplasmic Matter enveloping the Starch Granules. In order to demonstrate this clearly, the starch granules must be removed without disturbing the protoplasm. This can be done by means of the action of saliva, as this secretion contains an enzyme-ptyalin—which is able to dissolve starch, but has no action on protoplasmic matter. Prepare 3 or 4 c.c. of saliva by washing out the mouth with a very little water. (As the secretion appears to be more active before meals it is better to obtain it then.) Filter the solution into a test-tube, place

several thin transverse sections of barley in the liquid, and keep it at a temperature of 46° C. for three or four hours by immersing it in a vessel of water maintained at the desired temperature. (If the solution is kept for more than a few hours, which may be necessary, a little chloroform water should be added to prevent the growth of microorganisms.) When the action of the ptyalin is complete the original white appearance of the section, due to the presence of starch granules, will have disappeared. Now, place one of the starchfreed sections in a very dilute solution of eosine to stain the protoplasm, transfer the section to a slide, and examine it under the microscope. It will be noticed that the thin-walled cells are filled with a network of red-stained protoplasmic matter which originally enclosed the starch granules. The cavities in which the starch granules formerly lay will be clearly seen. A permanent mounting of

the section in balsam should be made after first very gradually dehydrating the section with alcohol of increasing concentration.

PART III.

EXPERIMENTS CONNECTED WITH THE TECHNICAL STUDY OF BARLEY AND OTHER CEREALS.

Study the Microscopic Appearance of Some of the Commoner Kinds of Starch.-The starches of barley, wheat, potato, rice and maize are suitable for this study.

Transfer a little of the starch to a drop of water on a glass slide, cover with a thin glass and examine with a high power. Observe the characteristic appearance of the different kinds of starch granules and make a drawing to scale of each. If the starch used has been obtained direct from the grain it is desirable, after examining in water alone, to stain with a little iodine solution; as the starch granules alone are stained blue, this differentiates them from other organic matter which may be present. By this means also the mixture of very small granules of starch with much larger ones, as in the case of barley starch, will become more evident.

Prepare a Sample of Starch from Barley or Other Grain.-Grind about 100 grms. of the grain to a very fine powder and mix with cold water. Separate the starch from the husk and tissue of the grain as far as possible by filtering the milky liquid through very fine muslin. Allow the starch to subside from the filtrate, pour off the liquid, and