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Research Bulletin (Iowa Agriculture and Home Economics Experiment Station)

Abstract

1. A gene influencing the strength of culm in maize has been isolated and found to behave as a simple Mendelian recessive. The character has been called lazy and the factor pail' involved has been degignated La la.

2. Lazy plants are distinguished from their normal sibs by their prostrate habit of growth. Their culms have a much lower breaking strength.

3. The culms of the lazy and normal plants have similar morphological structure, but differ histologically in the thickness of their cell walls.

4. The gene, lazy, exerts a marked influence on the composition of the culm. It greatly restricts the deposition of such structural materials as cellulose, lignin and pentosans. Lazy culms contain more moisture per unit weight of green tissue. During early development they also contain smaller amounts of nitrogen, water soluble material and total ash constituents on a green-weight basis.

5. Both the primary and secondary layers of the cell walls in corn become heavily lignified. All parts of the cell walls from the culms of normal plants contain much more lignin than do those of lazy plants. These differences are more apparent in the younger tissues.

6. The sequence of lignin formation is similar in normal and lazy culms. In parenchymatous tissues of both kinds of plant lignification apparently originates in the primary wall and later extends thru the secondary walls. In sclerenchymatous tissues the reverse relationship exists.

7. The lignin in the middle lamella and in the secondary walls differ in its structural appearance, the former being fibrillar and the latter granular in appearance.

8. All parts of the cell walls from the culms of lazy plants appear to contain less cellulose than do those of normal plants. The middle lamella of the young tissues of both normal and lazy plants appeared to be of a cellulosic nature and not pectinaceous.

9. The expressed juice of the lazy stalks contains a smaller quantity of ash and total solids. Its osmotic pressure is somewhat lower than that of the normal sibs. The ionizable constituents in the tissue fluids of the lazy culms, as shown by electrodialysis, also are lower.

10. The data indicate that the prostrate habit of growth, characteristic of the lazy plants, is due to a physical ralationship between the strength of the supporting tissue and the weight of the plant to be supported. This relationship evidently results from a restricted deposition of the structural materials of the dry matter per unit weight of green material.

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