Origins of Heterospory and the Seed Habit: The Role of.
Seed Habit in Pteridophytes: The adoption of heterospory and the retention and germination of a single megaspore within megasporangium to form a female gametophyte, led to the phenomenon of “seed habit”, a characteristic feature of the spermatophytes. A seed is that ovule which contains an embryo developed as a result of fertilization.
Heterospory and Seed Habitat (Origin of Seeds and Seed Habitat in Vascular Plants from Heterospory) Heterospory is the production of two or more types of spores Heterospory is a condition of the production of more than one type (usually two) of spores in a single plant.
Origins of Heterospory and the Seed Habit: The Role of Heterochrony. Login.. Heterospory and gametophytic unisexuality are not necessarily evolutionary antecedents of endospory; rather, they may have arisen as developmental consequences of endospory.. Origins of Heterospory and the Seed Habit: The Role of Heterochrony. Login.
Origins of Heterospory and the Seed Habit: The Role of Heterochrony. Summary The origin of the seed-plant life history, and subsequent diversification of seed morphology, should be considered two independent, fundamentally distinct evolutionary problems.
The existence of heterospory has importance in the origin and evolution of seed. Thus the origin of the seed habit is a logical progression that began with homospory, was followed by stages of heterospory, and culminated into the seed. Incipience of Heterospory.
Origins of heterospory and the seed habit: the role of heterochrony.
To understand the underlying causes of this highly iterative evolutionary pattern, Bateman and DiMichele (1994b) dissected heterospory and the seed habit into 12 phenomena that were more discrete and definable, and then sought repetitive patterns among the putative phylogenetic lineages. The maximum number of heterosporic phenomena acquired by each lineage is summarized in Fig. 3.
The zygote develops into the future sporophyte. The evolution of the seed habit is related to the retention of the megaspore. Heterospory is thus considered an important step in evolution as it is a precursor to the seed habit. Heterospory evolved first in pteridophytes such as Selaginella and Salvinia.
What is seed habit in Pteridophytes? In the seed bearing plants there are two kinds of spores: microspores and megaspores that grow to form male and female gametophytes.
Common character found in heterospory and seed habit - 11696799.
HETEROTHALLY AND THE SEED HABIT VERSUS HETEROSPORY. R. B. THOMSON. Department of Botany, University of Toronto. Search for more papers by this author.
The heterospory is noticed in seven genera such as Selaginella, Isoetes, Marsilea, Salvinia, Azolla, Renellidium and Pilularia. The heterospory results in the formation of seed habit. The megaspore containing the female gametophyte derives food from the sporophyte. As it remains inside the sporophyte it is independent of external conditions. It.
Since current hypotheses aim to find the phylogenetic origin of the seed habit in the free-sporing heterosporous, haploid dioecious condition, the importance of studies that determine the similarities and distinctions, both in structure and behaviour, of sexually differentiated sporangia at all levels, needs no further emphasis.
