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PHYCOLOGICAL SOCIETY OF AMERICA
P
lysiphnia
Polysiphonia is a small alga; most of the species used in this study were approximately two to ten centimeters tall. Therefore, most aspects of its morphology are only visible under the microscope. Click on the links below to find out about aspects of Polysiphonia's morphology:
Polysiphonous contruction is one of the most noteworthy characteristics of Polysiphonia. Apical cells cut off proximal segments which elongate to become axial cells. These cut off pericentral cells of the same length. The central axial cell is now surrounded by pericentral cells of the same length, forming one “tier” or segment. Polysiphonia can have four to 24 pericentral cells present per tier.
A pit connection consists of an opening in the cell walls of two adjacent cells which is filled with a plug and plug cap. Pit connections have a somewhat misleading name because there is not an actual connection or transport of material between the cells. Pit connections may lend support ato the thallus of the algae. The pit connections between pericentral cells and axial cells form during cell division and are referred to as primary. The pit connections between pericentral cells and other pericentral cells are referred to as secondary. This picture is an example of a secondary pit connection.
The dividing cells
in Polysiphonia are localized in the apical regions. In this
picture of the tip of a branch, you can see newly formed cells branching
on the left, and slightly older cells beginning to form"tier" structures
to the right.
Polysiphonia has
monopodial branching, which means that the primary axis remains the
main line of growth throughout the life of the alga, with secondary
branches forming off of the main axis. Branching is radial; branches
form in multipe planes rather than in just one. Exogenous branches
arise from segments immediately below the apical cell and cut off before
pericentral cells cut off from the axial cell; these are more common
in Polysiphonia than endogenous
branches, which arise
from the central
cell after the pericentral cells have been cut off
Trichoblasts are colorless hair-like filaments which cut off from the apex of the alga exogenously. On the left, you can see trichoblasts amongst some spermatangium on the apex of a male gametophyte. The sexual organs are borne on trichoblasts. Oftentimes, trichoblasts are deciduous, leaving behind scar cells (the trichoblast's basal cell). On the right, you can see scar cells between the polysiphonous tiers. Earlier, the trichoblasts existed in these positions and marked the apex of the alga. But since then, more tiers have been added and the trichoblasts have fallen off, leaving the scar cell.
Trichoblasts (left)
Scar cells (right)
Polysiphonia Morphology | Life History | Taxonomy | Ecology
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© Sarah Skikne 2000