WHAT ARE ROOT-HAIRS? (XXVII-2)

The problem. In the case of the carrot or beet used in the preceding experiment all of the smaller rootlets had been removed, but the remaining parts were still able to absorb water. Actively growing plants, how

wide. Turn, and crease one fold again, thus making a short fold each side of which is one inch in width. With a needle or pin perforate the crease of the short fold in many places, and place seeds in this fold. Place the filter paper with the wide fold innermost around the upper inner wall of the drinking-glass, allowing the ends to fit together. In case a funnel is used instead of a glass, the paper is folded and the apparatus set up as shown in figure 45.

2. Put some seeds between the filter paper and the glass. Fill the glass with sand or sawdust almost to the fold. Pour water

into the glass until the lower part of the wide fold is wet. The water will then cause the filter paper to adhere to the glass and moisten the seeds.

3. Observe from day to day, and as they develop, diagram and describe the roots and root hairs with reference to size, general appearance, length, diameter of hairs, location of hairs on roots, and abundance of hairs.

Questions. What differences are there in the length of root hairs on different parts of the rootlet? Are these differences due to differences in age?

Suggestions for report. Diagram the apparatus used and at least three stages in which the seedlings are sufficiently developed to show the root hairs. Write a complete description of the experiment and refer to the diagrams when necessary.

Reference work. Read sections 325 to 329.

Optional problems. If a microscope is available, mount some of the root hairs, together with the root from which they grow, and make a detailed study, showing the exact relation which exists between the root hairs and the surface cells of the root. Determine where the young root hairs are developing.

Stand freshly cut leafy stems in a red-ink solution. Very leafy stems, if placed in a sunny location with good circulation of air, may be ready for examination in half an hour. In many cases it will be well to allow the material to stand until the next day. Examine the stems by cutting across the stem at intervals or by peeling off the surface. If blanched celery, yellow coleus, or other light-colored plants are used, the stems will be sufficiently transparent to show the red color without cutting. Can the course of the solution be traced into the leaves? Are there definite tissues through which the solution passes? Diagram a cross section of the stem and a surface view of a leaf to show any points observed regarding definite tissues through which water passes.