PLATE XVIL— COMMON MUSHROOM (Agaricus campestris) and RED SEA- WEED (Polysiphonia). 



Mushroom. 



The Pezizae are distinguished by producing their spores in the interior of cells called Asci, and the Mushroom produces its spores 

 on the exterior of enlarged cells called Basidia, hence the name applied to the group — Basidiomycetes. The common Mushroom may 

 be found towards the end of summer in open pastures, but it can be raised from spawn at any season of the year. Mushroom spawn 

 simply consists of the mycelium mixed up with decaying organic matter, and under proper treatment, as to moisture and temperature, 

 mushrooms may be produced. 



Although the mushroom belongs to the most highly organised group of Fungi, just as the Red Sea-weed belongs to the highest 

 group of Alga, yet no sexual stage has yet been discovered. 



Fig. 1. Mushroom, full grown. 



The mycelium consists of interlacing threads spread out in the mould, and what is called the Mushroom is 

 really the Spore-fruit arising from this mycelium. 



Spore-fruit composed of — Stalk with a remnant surrounding it near the top, of what once extended to the 



margin of the Cap. 

 Cap spread out like an umbrella, and bearing on its under surface the radiating 

 plate-like Gills. 



Fig". 2. Young Mushroom, entire and in section. 



The cap and stalk are already roughly indicated. 



The section shows the commencement of the gill-chamber, which is really a hollow ring in which the gills are 

 formed. 



Fig. 3. Mushroom more advanced — in section. 



Velum (Lat. a veil), forming a floor to the gill-chamber from the roof of which the gills are developed. 



Fig. 4. Remove a gill, embed it in paraffin, and make a section of it. 



The centre is occupied by mycelial filaments closely packed and adhering side by side, and towards each 

 surface this tissue becomes denser on the outside, giving rise to the Basidia. 



Fig. 5. Section under high power. 



Towards the surface the cells get rounded, and the superficial layer of cells is enlarged to form Basidia. The 

 Basidium has four slender processes (two only shown), at the ends of which the spores are developed and easily 

 detached. 



Fig. 6. Germination of Spore of Coprinus. — The spores . may be readily obtained by laying the Spore-fruit upon a sheet of 

 paper, then by placing over the spores a glass slide moistened by the breath, they may be lifted up and examined. 

 The spore placed in a drop of an appropriate fluid on a slide begins to germinate in a few hours by putting 

 forth a delicate filament. This grows, becomes divided by transverse partitions and branches, thus forming a 

 mycelium. In the course of from nine to twelve days the Spore-fruit arises directly from the older mycelial 

 filaments. 



Fig. 7. In some cases, however, a Sclerotium is formed first. — This consists originally of an aerial branch, which divides and 

 branches on all sides till it forms a small ball of closely packed and interosculating filaments. One of the surface- 

 cells grows out and becomes the young spore-fruit, which, in this instance, is entirely invested by the velum. 



Life History. — It is very tempting to suppose that the Spore-fruit is the result of a sexual process, but as experiments specially 

 directed to that point have failed to show any trace of it, it is now generally believed that in the whole of the Basidio- 

 mycetes the Spore-fruit arises directly from the mycelium or indirectly from a Sclerotium. 



The stages through which they pass would be briefly as follows : — the Mycelium (or Spawn) produces a Spore-fruit 

 directly, which bears the numerous spores from which the mycelium is again produced, and so on ; or, in some cases, the 

 Spore-fruit is preceded by a Sclerotium. 



Red Sea-Weed. 



Polysiphonia (Gr. polus, many ; siphon, a tube) is one of the Red Sea-weeds — plants usually of a graceful form and beautiful colour, 

 so that they attract attention. This form is found about low-water mark, attached to rocks, the stalks of the Tangle, etc., and although 

 so finely divided, it may be removed from the water without collapsing. These divisions might be regarded as of the nature of leaves, 

 just as in the next form considered (Chara). There are three distinct forms of this plant, all agreeing in general appearance, but 

 differing in their reproductive habit — the Non-sexual, the Male and the Female; and it is the first of these which will be considered 

 now. 



Fig. 8. Plant much divided. 



Fig. 9. Plocamium is one of the feathery red sea-weeds, and when simply spread out in water under the microscope, it shows 

 clearly the single growing cell — cells a little further back dividing longitudinally to produce breadth, and a single 

 cell growing laterally and dividing to form one of the numerous branches. The cell-walls are gelatinous. 

 Fig. 10. Portion of Non-sexual plant showing Tetragonidia 



They appear as little round balls, but under a high power division is seen. The four gonidia do not lie in 

 one plane, but are arranged like a tetrahedron; hence, either one or three divisions may be seen. 

 The gonidia escape by a parting between the peripheral cells. 



Fig. 11. Germination. — The Gonidium elongates, divides transversely, one of the divisions serving for attachment, the other 

 growing and dividing longitudinally and transversely, and branching, till it becomes a parent plant 



