Page:Encyclopædia Britannica, Ninth Edition, v. 3.djvu/712

694 And we may have every grade of development, from the simplest case, in which the sporocarp appears as a mere appendage of the parent plant of inconsiderable dimensions, to the most extreme condition in the other direction, in which the sporocarp is capable of independent growth, _ and therefore represents a second generation which is entirely distinct (sporophore). The sporocarp also differs essen tially from the oospore in the fact that cells contribute to its formation which have not been directly influenced by fertilization, and that in consequence the part of the fruit which produces the spores is surrounded by what for want of a more convenient term we may call the pericarp, in which no spores are developed, and which serves as a mere protective investment, or is subsequently drawn upon for purposes of nutrition. In Phycomyces, which belongs to Zygosporece, it is noteworthy that there is a kind of anticipation of the development of a protective investment to the zygospores. The principal types of the Carposporece include all the more highly developed forms both of Algce and Fungi. In Coleochcvtece the carpogonium terminates in an open canal, and fertilization is effected by motile antherozoids. In Floridece, in the simplest type (JVemalion), the car pogonium resembles that of Coleochcetece, only the terminal tube (trichogyne) is closed and not open. Fertilization is effected by passively motile antherozoids, which adhere to the trichogyne. In Ceramiece the carpogonium, even before fertilization, consists of numerous cells, a lateral row of which the trichophore bears the trichogyne. Neither trichogyne nor trichophore, however, take any part in the de velopment of the sporocarp. The pericarp is produced by a process of budding from cells beneath the carpogonium. In the genus Dudresnaya the process of fertilization be comes very complicated, and in fact involves a double pro cess, of which the first stage consists in the application of antherozoids to a trichogyne ; and the second in the de velopment from below the trichophore of a &quot; conducting filament&quot; which conveys the fertilizing influence to the terminal cells of a number of small branches, with which it successively conjugates; at each point of conjugation a sporocarp is developed. Amongst the Ceramiece there is something comparable to this double process ; the fer tilizing influence which is conveyed by antherozoids to the trichogyne must afterwards be communicated by a process of diffusion from the trichophore to the cell from which the spores are developed. Characece are now to be regarded as a reduced type of Carposporece. The carpogonium is supported by two basal cells with oblique septa, which it seems quite reasonable to accept as the rudiments of a trichophore. There is, of course, no trichogyne, and fertilization is effected by motile antherozoids, and the pericarp is developed before instead of after this process. In Cham the main axis is clothed with a peculiar cortical tissue, which grows over it from the nodes, and_is clearly comparable with that which exists in the Ceramiece. Fungi contribute to the Carposporece the Ascomycetes, JEcidiomycetes, and Basidiomycetes. In the first and last of these groups the existence of a sexual process preceding the development of the sporocarp is now known. Ascobolus has been studied by Janczewski, and the essential features of the sexual process are closely comparable to those of Ceramiece. The carpogonium consists of a row of cells ; the terminal one is fertilized by the ramified &quot; pollinodium,&quot; and from the central cell of the carpogonium a number of filaments branch out which bear the asci, while the peri carp is formed by the branching of the mycelium below the carpogonium. Lichenes, in so far as the hyphse and fructification are concerned, are essentially ascomycetous fungi. Their gonidia are referable to different groups of algse. The two sets of organisms live together in a kind of modified com- mensality. The algae are able to sustain their companion fungus without succumbing to the demands of its nutrition.

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Alternation of generations exists amongst the Thallo phyta. But, as in GEdogonium, it assumes the form of an occasional occurrence of gamogeuesis after more or less prolonged periods of agamogenesis ; a series of sporophores is interrupted by the intercalation of an oophore. Amongst the Cormophyta, however, we have generally a regular alter nation of oophore and sporophore. Both may, however, propagate themselves by the detachment of more or less specialized gemmae. But apart from this, the agamogenetic production of spores and the gamogenetic production of oospores regularly follow one another. Cohn, in a classification of Cryptogams published in 1872, established the groups Bryophyta and Pteridophyta, which, added to Phanerogamce, constitute the groups into which Cormophyta appear best susceptible of division.

1. Bryophyta.—In such a case as (Edogonium, sporophore and oophore each attain a tolerably equal degree of vegetative development. In others, however, this may be very much curtailed in one or the other generation. Amongst the Thallophyta the sporophore not uncommonly suffers this reduction. Thus in Mucor the zygospore only develops a short filament, which terminates in a spo rangium filled with spores. If we suppose the filament suppressed, the spores belonging to the second generation will . be produced directly from the oospore itself. Thus, amongst the Ccelollastcc, in Cystopus the oospore produces zoospores, and, according to Cienkowski, this is also the case with Volvox. In such cases the oospore itself is the sporophore. Amongst the Bryophyta there is an alternation of generations which is hardly less abridged. The oophore which in Hepaticce is often a thalloid body, while in mosses it is a leafy plant bears female organs (archegonia) and male organs (antheridid). The oospore, or fertilized central cell of the archegonium, gives rise to a complicated struc ture which produces the spores. The first division of the oospore appears to be inclined to the axis of the arche gonium. The sporophore is retained in a kind of attach ment to the oophore, and never attains to any vegetative development of its own. From the fact that the vege tative structure of some Hepaticoe is thalloid and leafless (Ancura), while in others (Marchantia) leaves are present in a very reduced condition, it may be inferred that the former have lost their leaves rather than that they repre sent an original leafless condition. The ancestral type of the Bryophyta was probably more like a moss than like any of the Hepaticce. And it is worth while considering what claims Chora may have to be regarded as a transition from the Thallophyta, of which it is an anomalous type in its possession of distinct lateral appendages to the axis. Cohn placed it amongst the Bryophyta; but its removal to the Thallophyta probably assigned it its true position. The investment of the carpogonium, however, cannot have more than an analogy with an archegonium. The fertilized carpogonium (sporocarp) might perhaps be regarded as a very reduced form of that of the Bryophyta, producing only a single spore. It is certainly an interesting and it may be a significant point, that the spore of Cliaracece produces in germinating a filamentous chain of cells, appa rently comparable to the protonetna of mosses, and from this the fully developed sexual plant is produced as a lateral bud.

2. Pteridophyta are sharply divided from Bryophyta by the high vegetative development of the sporophore and 