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Heterospory is the production of spores of two different sizes and sexes by the sporophytes of land plants. The smaller of these, the microspore , is male and the larger megaspore is female. Heterospory evolved during the Devonian period from isospory independently in several plant groups: the clubmosses , the ferns including the arborescent ...
Spores of two distinct sizes (heterospory or anisospory): larger megaspores and smaller microspores. When the two kinds of spore are produced in different kinds of sporangia, these are called megasporangia and microsporangia. A megaspore often (but not always) develops at the expense of the other three cells resulting from meiosis, which abort.
Diagram showing the alternation of generations between a diploid sporophyte (bottom) and a haploid gametophyte (top) A sporophyte (/ ˈ s p ɔːr. ə ˌ f aɪ t /) is the diploid multicellular stage in the life cycle of a plant or alga which produces asexual spores. This stage alternates with a multicellular haploid gametophyte phase.
In the mathematical discipline of graph theory, a graph labeling is the assignment of labels, traditionally represented by integers, to edges and/or vertices of a graph. [1] Formally, given a graph G = (V, E), a vertex labeling is a function of V to a set of labels; a graph with such a function defined is called a vertex-labeled graph.
Such tissue is commonly formed, for example, at the base of a petiole or pedicel. acaulescent Having no apparent stem, or at least none visible above the ground surface. [2] Examples include some species of Oxalis, [5] Nolina, [6] and Yucca. [7] Antonym: caulescent (possessing stem). accrescent
However, not all heteromorphic gametophytes come from heterosporous plants. That is, some plants have distinct egg-producing and sperm-producing gametophytes, but these gametophytes develop from the same kind of spore inside the same sporangium; Sphaerocarpos is an example of such a plant. In seed plants, the microgametophyte is called pollen.
Layered graph drawing or hierarchical graph drawing is a type of graph drawing in which the vertices of a directed graph are drawn in horizontal rows or layers with the edges generally directed downwards. [1] [2] [3] It is also known as Sugiyama-style graph drawing after Kozo Sugiyama, who first developed this drawing style. [4]
Paleontologists can take advantage of diagrams for reconstruction of fossil flowers. Floral diagrams are also of didactic value. [1]: xiii Relation of a plant material (Campanula medium) to the floral diagram. Black dashed line shows the cross-section. 1 – position of the main axis; 2 – cross-section through the lateral flower; 3 ...