Tag: biology

In Funaria, spore has small irregular mitochondria, numerous chloroplasts with poorly developed lamellae, small sparsely present dictyosomes and ER in the form of highly convoluted tubules near the plasma membrane.

The mature sporophyte of Funaria is much more complex than that of the liverworts. It is differentiated into foot, seta and capsule. The foot forms the basal portion of sporophyte. It is a small, dagger-like conical structure embedded in the tissue of the tip of the leafy female branch and functions both as an anchorage and an absorbing organ. The seta is a long cylinder but tough, reddish brown, stalk-like structure. It carries the capsule at its top and raises it more than an inch above the apex of the leafy gametophore. The capsule is a highly organized structure. It is pear-shaped and green at first but later turns yellow, and then orange. Its upper portion is covered by a conical hood or a cap, the calyptra. At maturity, the calyptra falls off laying bare its apex. 

Sphagnum has no seta. In Sphagnum and other basal mosses, the sporophyte is raised by the pseudopodium, a structure produced by the parent gametophyte.  

The sporophytes of mosses, like those of the liverworts, consist of a foot, seta and capsule and remain permanently attached to the gametophytes. At the tip of the capsule is a lid (operculum) which, prior to spore dissemination, falls away exposing the so-called peristome teeth, a set of structures, often delicate and thread-like in appearance, that form a ring around the mouth (rim) of the capsule. The peristome teeth are perhaps the most characteristic feature of the mosses; usually composed of cell wall remnants, they respond to changes in the humidity of the atmosphere. When a moss first grows from the spore, it grows as a protonema, which develops into a leafy gametophore.

The peristome, which lies immediately below the operculum consists of two sets of long, conical teeth, one within the other. The teeth of both the sets are on the same radii and thus opposite to each other. The tapering distal ends of the teeth of the outer set converge towards each other and are united terminally in a small central disc of tissue. The peristomial teeth are sculptured structures, that close the opening of the spore sac. They are attached at the base of the rim or diaphragm. The outer set of the peristomial teeth are hygroscopic and respond to the changes in humidity. The presence of peristomial teeth guarding the mouth of the theca region slows the rate of spore discharge.

The hygroscopic movement performed due to imbibition of water is called as hydrochasy. E.g., movement in the peristome of moss, elators in eqisetum. 

In Sphagnum, the stems themselves show a greater degree of internal complexity than most other mosses. The stem tissue can be divided into two regions, an inner pith (which may be subdivided into two layers) and an outer cortical layer of larger, usually dead cells. The pith is the site of food production and storage, which the cortical layer functions in water absorption and protection. Located in the cortical layer of many species are retort cells, so named, because they resemble the medieval chemical flasks called retorts. These cells are enlarged more than the surrounding cortical tissue, and have a pore, or opening, at one end. These cells are believed to help the moss retain water under intense sunlight, and they often are home to a wide variety of small invertebrates and other microorganisms.

Ferns and moss are both examples of 'primitive plants'. They have not developed all the specialised systems, that modern plants have, although ferns are more highly developed, than mosses. In mosses, sporophytes lack chlorophyll and depend on photosynthetic gametophyte for food, whereas, in ferns, sporophyte stage has true roots, stem and leaves and does not depend on gametophyte.

Capsule wall surrounds a wide air space. It is traversed by multicellular, narrow, uniseriate, green, elongated filamentous strands, known as trabeculae. Trabeculae connect the chlorenchymatous layer of wall with the spore sac.