Fig. 266.—Cladostephus spongiosus
Fig. 267.—Chordaria flagelliformis
In the genus Elachista there are some very small and peculiar weeds that are almost sure to be overlooked by inexperienced collectors. They are parasitic, and are composed of two kinds of jointed threads, the inner of which are forked and combined into a tubercle, while the outer are simple and radiate from the tubercle. The spores are attached to the inner threads. The largest species (E. fucicola) is parasitic on Fucus, growing in brush-like tufts about an inch long. Some of the smaller ones are mere star-like tufts of no attractive appearance, and would be disregarded as troublesome parasites by most young collectors, but all of them are very interesting objects for the microscope.
The members of the genus Myrionema are similarly liable to be neglected, for they are minute parasites appearing only as decaying spots on larger weeds, but nevertheless form interesting studies for the microscope. Like the last group, they have two sets of jointed fibres, the inner being branched, and spread over the surface of the plant on which it grows, while the outer are simple and stand out at right angles, but all are united into a rounded mass by a gelatinous substance. Perhaps the best known is M. strangulans, which infests Ulva and Enteromorpha, producing the appearance of small decaying spots.
In the genus Leathesia we have other unattractive weeds, the jointed and forked threads of which are all united together into tuber-like fronds that are common on rocks and weeds between the tide-marks. There are three or four species, all similar in general appearance, with the spores distributed among the outer threads. These weeds cannot be satisfactorily pressed and dried in the usual way, and should be preserved in formaldehyde or dilute spirit, when they will always be available for microscopic examination.
The last genus of the Chordariaceæ is Mesogloia, so called because the central axis of loosely-packed, interlacing threads is covered with gelatinous substance. Around this axis there are radiating, forked threads which are tipped with clubbed and beaded fibres among which the spores are distributed. One species (M. vermicularis), common in most rock pools, is of a wormlike form, of a dirty olive or yellow colour, with soft, elastic fronds growing in tufts from one to two feet long. M. virescens, also a common species, is of a pale greenish or olive colour, and very soft and slimy. Its stem is round and slender, freely branched, with short, simple branchlets.