Page:Encyclopædia Britannica, Ninth Edition, v. 9.djvu/870

 834 FUNGUS by one cell, but after fertilization a transverse wall divides it into two cells, the inferior one of which must be regarded as an ascogenous hypha. The superior one becomes the ascus, which in most cases contains 8 spores. In a few other forms several asci are formed by the carpogonium. The species of Eurotium e.g., E. repens and E. (Axper- r/illus) f/laucus agree in the more striking details of their life-history with those of Erysiplie. The mycelium may be found as a fine flocculent mass on the surfaces of most putrefying organic matter. The usual and most extensive mode of reproduction is by the conidia, which are formed in great abundance at the apex of the conidiophores. These germinate and grow under most varied conditions, which fact, coupled with their plentiful production, explains the general distribution of the fungus. Subsequently the sexual organs arise on the same mycelium. The carpo gonium is the end of a mycelial hypha wound up in the form of a corkscrew, with a tranverse septum at each turn of the screw. From the lowest turn two tubes sprout and grow up on the outside of the carpogonium ; one always grows more rapidly than the other, and reaches the top of the carpogonium, which it fertilizes. This is the pollinodium. Other cells then grow out from the bases of both organs and envelop them. After fertilization the carpogouium divides into several cells from which the ascogenous hyphse arise. The asci contain ascospores which germinate as in the other Erysiph M. The whole fructification is called the pen- thecium. Suborder III. Tuberacece. The mycelium of the Tuber acece is in most cases small in comparison with the fructi fication. This fructification consists usually of a large sub terranean tuberous body, possessing a thick wall of pseudo- parenchyma, and enclosing a dense mass of hyphse, among which the ascogenous filaments produce the asci embedded in sterile paraphyses. Conidia are known only in the case of Penicillium glaucum, a fungus which, from its common occurrence, and its being well-known in all its stages, may be chosen as a type of the suborder. Its mycelium inhabits almost any organic substance, and produces on erect coni diophores long chains of conidia in very great abundance. It is only in darkness that (as in the other Tuberacece) the sexually produced form of fructification arises. The sexual organs resemble in a very high degree those of Eurotium (see preceding suborder), but the development of the fructi fication after the ascogonium has been fertilized is totally different from the corresponding process. After the asco gonium has begun to germinate, the growth of the envelop ing hyphaj so hinders this process that it is forced to rest in a sclerotioid state. If germination, however, be en couraged by artificial means, the ascogenous hyphse force their way out and form asci, in each of which there are 8 ascospores. These spores, on germinating, produce a mycelium which bears conidia. If the germination of the sclerotia be delayed so long that the ascogenous hypha} lose the power of producing asci, the enveloping filaments give rise to the conidial form of fructification. The structure of these sclerotia is so similar to that of the well-known tuberous fructifications of the Tuberacect; that Brefeld, who discovered them, classes Penicillium with this suborder, in spite of the very strong resemblance of the sexual organs to those of Eurotium. In no other species of Tuberacece has this life-history been observed. Suborder IV. Pyrenomycetes. The Pyrenomycetes pro duce their asci within round or flask-shaped perithecia, with walls of pseudo-parenchyma. The asci contain, as a rule, 8 spores. In some cases the perithecium is open at first, but in others the neck, closed during the earlier stage, forms subsequently a canal through which the spores escape. In the case of the Sphwriw simplices, the perithecia arise on a very fine mycelium, and according to Woronin and others are the result of a sexual act In Xylaria and allied genera, however, the perithecia are formed on sometimes very large club or basin shaped bodies, consisting of dense masses of tissue, which, according to some, are simply the receptacles, and according to others, bearers of sexual organs, the union of which gives rise to the perithecia. Analogy leads to regarding them as receptacles. Conidia are formed not only on the mycelium but also on the stroma, and even occasionally on the hyphse composing the wall of the peri thecium. Spermogonia and^ycwiV/i a are other conceptacles which give rise to asexual organs of reproduction, called re spectively spermatia and stylotyores. It was urged with much show of probability that these were parasitic bodies but the recent researches of Dr Bauke on the 2^ycnidia and M. Cornu on the spermatia seem to disprove this view. M. Cornu states that he caused spermatia to germinate and reproduce the mycelium of the species to which they be longed. It will be seen, however, that in the next suborder (LicJienes) the analogous spermatia act as male organs, a function which not only precludes the possibility of their parasitic nature, but does not agree well with M. Cornu s (so far as we know) unconfirmed views. In Claviceps pur- purea (ergot), which attacks the young ovary of rye, the mycelium first bears conidia embedded in a mucous secre tion; this is called the spkacelia stage. The mycelium, however, soon permeates the ovary and forms a hard sclerotium the ergot stage. After undergoing a period of rest, usually from summer to spring, but varying in length, the sclerotium on falling on damp ground pushes out small stalks with a rounded head in which numerous flask-shaped, wall-less perithecia arise. These perithecia bear as usual asci containing ascospores. The ascospores, on germinating, and finding their usual host the rye, or some nearly related grass, give rise again to the sphacelia, which closes the cycle. This suborder, like the Discomycetes, contains a great number of forms, many of which are known in only one, viz., the perithecium-bearing stage, the other phases probably being known by other names as distinct genera and species. The Pyrenomycetes grow either on dead organic matter or on the bodies of living plants. Suborder V. Lichenes. Until recently, and before their true nature was understood, the Lichenes were treated as constituting a separate class of cellular cryptogams or Thallophyta. The researches of Schwendener, Stahl, L)e Bary, Bornet, and others have proved that these consist of a fungal Ascomycetous element parasitic on an algal element. The algal element belongs to the lower orders of Algca and acts as the nourisher of the fungal element. The fungal element is reproduced by Ascomycetous reproductive organs, and the algal element, which in a free state is capable of independently subsisting, is reproduced in the manner characteristic of the order of Algce to which it belongs. We have to do here with the life-history of the fungal por tion only, but illustration will be given of its relations with its host. Though sexuality is not known to exist generally in the Lichenes, it has been so satisfactorily proved in the case of the Collemaccce by Dr Stahl that it may be concluded that investigation only is necessary to bring fresh cases to light. In the Collemacece the male organs of reproduction (the sj)ermatia) are formed within receptacles called spermogonia (similar organs have been described ;as occurring in the Uredincce, &c.), and though not possessing the power of spontaneous motion, reach the female organ (trichogtjne) by the agency of water or the atmosphere. The spermatia consist of one simple minute cell ; the trichogynes are of a more complicated structure, and may be described as con sisting of a unicellular organ of conception, a conductive canal, and an ascogonium, consisting of a coiled hypha of several cells. The point of the trichogyne emerges from the