A manual of British lichens : containing descriptions of all the species and varieties / by William Mudd.

  • Mudd, William.
Date:
1861
Catalogue details

Licence: Public Domain Mark

Credit: A manual of British lichens : containing descriptions of all the species and varieties / by William Mudd. Source: Wellcome Collection.

    21/356 (page 9)
    the cxcipulum is altogctliev wanting, as is sometimes the case Chi- odecton, &c.), each part then performs its own functions, and remains separate, e.(]. several Lccideat, Gn/jj/iis. &c. Perithecium. This, in the angiocarjious division, is analogous to the excipuhim in the gymnocarpons, and does not differ from it, except in form. It usually constitutes the shell or outer covering of the apothe- cium, which in general assumes a globular, hemispherical, or hemisplie- rico-convex figure. Tn a globular or globose apothecium, the j^erithecium entirely envelopes the nucleus {pei'iihecium entire) ; in an hemispherical one, only the upper or exposed part (2)ei-ithecmm dimidiate), the base of the nucleus being then enveloped in a thin inner tunic or internal lining of the perithecium ; this internal lining, in the entire perithecia, is not always distinguishable, as it is, to a greater or less extent, incor- porated with the perithecium itself, but it is more than probable that it is always jjresent. The apex of the perithecium (usually designated osfiolum) is, for the most part, slightly depressed ; it is generally de- scribed as being perforated by a simple jiore, but this expression is not literally correct, as the minute opening of the ostiolum is invariably at first covered with a thin, gelatinous veil, Avhich protects the nucleus, and prevents the discharge of the spores until they arrive at maturity. 2nd. Thalamium. The thalamium comju-ises the organs of the fruit, and is that part of the apothecium which is contained in the excipulum. It is readily distinguished from both the cxcipulum and the hypothe- cium by being composed of different elements, and by their perpen- dicular position. It usually consists of erect paraphyses and asci, more or less conglutinatcd together with an amylaceous, mucilaginous, or watery substance, all of which greedily imbibe water. Nucleus. This differs in nothing from the thalamium, except in the figure and form of the paraphyses, which are most frequently hyaline, and linear throughout. The paraphyses are the fine hyaline filaments, which arise perpen- dicularly from the hypothecium, and are cemented to its superior face by a great number of very fine cellules. They are in general of an equal height, closely packed together, and usually very slender, but in this respect they are liable to some variation, yet rarely or never exceed •001 inch in thickness. They also assume difltrcnt forms, being some- times of a clavajform figure, at otliers linear, attenuated into a short pedicle at the base, and somewhat thickened at their apices ; at other times linear, and somewhat articulated ; and at times linear throughout. In general, it is not difficult to perceive that they arc hollow, and more or less filled with a mucilaginous, uncoloured substance {protoplasma), it being, at times, separated into little globules. Their apices are ordinarily coloured, and cemented togeth(!r with a sub-gelatinous sub- stance, which, through exposure to the influence of tlie atmosphere, becomes indurated to a greater or less extent; and which, gradually expanding with the growth of the thalamium, eventually constitutes that part which is commonly called the disc, {epiihccivm) in the descrij)- tive characters of the species. In some genera, the paraphyses are alto- gether wanting, their place being su])plied by a greater abundance of the mucilaginous or watery substance ; as in ArlJionia, etc., in the gymno- carpous division, and I^docarjxm, Verrucaria, etc., in the angiocar- ])OUS. The asci are large oblong, cylindrical, or clavrcform cells or vesicles,