Structure and Reproduction in Stemonitis.pptx

Stemonitis Life History

1. Stemonitis

2. Structure This is one of the most common Myxomycetes growing on dead wood and dead leaves. The plasmodium is of aphanoplasmcdium type. The colour of the plasmodium is usually watery to creamy-white, often may be pale-yellow . The Plasmodium does not possess the typical reticulated fans but is composed of network of fine strands. The young plasmodium consists of long main veins with branches here and there which bear secondary branches with some anastomosis . In the young, actively growing stage of the plasmodium, the; veins are almost completely devoid of an outer layer.

3. Structure Streaming of protoplasm is almost imperceptible in the smaller veins. Protoplasmic streaming, however, is very rapid and rhythmically reversible in the larger veins. The protoplasm is not very granular. As the plasmodium grows, it often spreads in thin, sheet-like, highly vacuolated areas. The plasmodium eventually be­comes concentrated into thick, blob-like masses which are transformed into sporangia.

4. The sporangia are attached in small clusters on a common hypothallus . They are cylindrical, stalked, and fasciculate. The solid stalk extends within the sporangium usually to near the apex as a columella . The capillitium is formed of numerous threads radiating from all parts of the columella and is combined into a loose network, the ultimate branches of which are united into a surface net. The surface net of capillitium may be complete or incomplete above. But the surface net may also be absent. Spores remain embedded in the capillitium .

5. The spores are abundant in a sporangium, and vary in colour, wall marking and size. They are grey, violet-grey, rufous -violet to pale ferruginous. The spore wall may be smooth, warty or reticulated. The dimension of spores usually ranges from 4 to 12µm in diameter. The mature spore on germination produces one or two swarm cells or myxamoebae . The fusion between the swarm cells or myxamoebae as the case may be, results in the formation of a zygote.

6. The zygote grows and undergoes a series of mitotic nuclear divisions developing into a plasmodium. Eventually the Plasmodium heaps itself up somewhat developing into sporangia. The nuclei within the developing sporangium undergo meiosis and a very large number of spores, each with a nucleus bearing haploid number of chromosomes is formed by cleavage of the protoplast. Simultaneously with the development of spores, the capillitium and columella also develop