Growth Factor Studies with Spirodela polyrrhiza (L.) Schlied

Citation

Gorham, Paul Raymond (1943) Growth Factor Studies with Spirodela polyrrhiza (L.) Schlied. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/H9KZ-FX44. https://resolver.caltech.edu/CaltechTHESIS:01242017-135027892

Abstract

Leeuwenhoek was one of the first men to record observations upon the peculiar growth habits of members of the family Lemnaceae. Taxonomists and morphologists have long argued about the proper classification and anatomical interpretation of these, most modified of higher plants, while physiologists from the time of Sachs have seen in Lemna and Spirodela a type of plant peculiarly suited for experimental investigations in the field of nutrition. This has been because of their small size and aquatic habit which make them ideal for culture in nutrient solution.

In recent times there has been considerable controversy over the question as to whether organic manures, humus, peat, and soil supply small amounts of organic materials which promote the growth of green plants. Are the beneficial effects often observed upon treatment with these substances simply the result of correcting recognized or unrecognized inorganic deficiencies, or are they the result of accessory growth factors?

In undertaking to answer this question, Spirodela polyrrhiza (L.) Schleid. was chosen as the test plant since careful control of its growth environment is readily achieved. The possibility of freeing the plants of microorganisms and employing sterile culture technique make its use particularly desirable in a study concerned with the effects of organic materials.

The primary aim in the investigation was to demonstrate that organic additions to a medium of inorganic salts balanced for optimal growth can produce a significant increase in growth. Also, that manures, humus, peat, and soil are sources of these growth promoting substances, and to find out as much about their nature as possible. Growing out ot this line of study was a broader one, namely, an attempt to gain some insight into the mechanism of the action and interaction of the many different factors, such as light, carbon dioxide, carbohydrate supply, etc., which are known to affect the growth of Spirodela. Finally, unsuccessful attempts were made to induce flowering of Spirodela, which occurs only rarely in nature and has never been induced experimentally.

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