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Studies - physiological and anatomical - on seeds

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OrrHR_1935redux.pdf (21.66Mb)
Date
1935
Author
Orr, Henry Richardson
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Abstract
 
 
The chain of connected processes and transformations which extends from the quiescent seed to the actively developing juvenile plant may be regarded, in general, as the phenomenon of germination. The first and most important of these changes, and the one upon which all the others depend, is the absorption of water. A study of this prerequisite for success in germination therefore seems fundamental to the elucidation of the entire process, more especially as the question of successful germination bears so definitely on many problems of practical agriculture, as well as on aspects of more purely academic interest.
 
Relevant to this main problem is the question of how substances dissolved or suspended in the water supplied to the seed affect this process. Here again, as in the main problem, points of academic interest arise, but these are overshadowed by more practical questions because of the increasing use of chemical dressings as preventives against the attacks of seed - borne and soil fungi. Another aspect of the problem is the mode of penetration of these added substances into the seed, where some fungus may be located, which the fungicide must reach if it is to accomplish its beneficial work.
 
This present thesis, therefore, is a report of studies on the intake of water by the seed, and the penetration of various substances dissolved in the water supplied to the seed and their effect on germination. It must be made clear that the work is, in the main, exploratory in nature for when initiated the whole conception of the initial stages of water intake by the seed had been recast by the researches of Nelson and MacSween on the Broad Bean, Vicia Faba L., published in 1933. Until that time the path of water intake had been defined as taking place through the micropyle, and the general surface of the seed had been regarded as of minor importance in so far as it affected the intake of water. That this conception is not true, at least for the earlier phases (the first six hours approximately), has been proved. The newer conception is that the first stage is the hydration of the testa, which, being of a colloidal nature, absorbs water by imbibition. The hydrated testa is known to be an imperfectly semi-permeable membrane, and it has been suggested that further water intake is by osmosis through this structure. Some doubt still exists as to the exact nature of the substance which acts as the "attractor" of the water through the seed-coat, but, in the main, the steps in the process as outlined by Nelson and MacSween hold good. A subsidiary point of considerable importance brought out by these workers is that each seed must be regarded as an individual, because when using genetically standardised material it was shown that while the curve of water intake by a seed of Broad Bean had characteristics similar to another seed, yet they differed in their relation to time. These differences may be, and probably are, related to the pre-history of the seed, e.g. maturation, storage, etc. (Hysteresis of the seed-coat colloids probably covers much of this).
 
URI
http://hdl.handle.net/1842/33434
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