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Title: Studies in the post-seminal developments of the monocotyledonous embryo
Author: Boyd, Lucy
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1931
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Abstract:
1. The main trend of the Monocotyledonous seedling is towards precocious development of the plumule, abortion of the radicle and consequent importance of an early adventitious root system. 2. The vascular tissue of the cotyledon is disappearing, a phenomenon illustrative of convergent evolution since it occurs in unrelated families. It may be regarded: - i. as a progressive tendency, because the plumule is thereby benefited; ii. as an indication that the Monocotyledons are a phylum of decadents, or the residuum of a stock now incapable of change save in the direction of reduction or curtailment. The wealth of structural detail revealed in the seedling is an added argument for this point of view. 3. The habit of the adult may act as a differentiating factor in three ways - i. as an aid to the reduction process. The equipment of the embryo and young seedling for a geophytic existence in the manner described is doubtless connected with increasing xeromorphy of the adult. ii. as a check on the reduction process, in order that organs necessary for the mode of life of the adult be retained, e.g. a lengthy tap root in young bulbous plants. iii, as a direct and forceful cause of reduction in individuals, e.g. aquatics and epiphytes, quite apart from its more ancient and widespread effect in directing in an almost imperceptible fashion the evolutionary trend. 4. To the voluminous literature on the origin of Monocotyledons there is little to add. The single cotyledon is undergoing reduction; it may be argued, therefore, that it arose primarily from the reduction or fusion of two cotyledons. If so, the assumption that such a union produced a central type does not account for the anatomy of primitive seedlings. The sequence revealed by this research points to the derivation of the phylum from an ancestor having numerous cotyledonary strands, or to the alternative of their polyphyletic origin.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (D.Sc.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.735215  DOI: Not available
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