Page:Encyclopædia Britannica, Ninth Edition, v. 24.djvu/143

VEGETABLE KINGDOM 127 ribbon-like, as in Dictyota, Phycoptcris, Dictyopteris, or broader and fan-shaped, as in Taonia, Padina, Zonuria ; usually attached by the base, but by root-hairs developed on the under surface in Zonaria. Asexual reproduction by spores, formed four (tetraspores) in each unilocular sporangium ; spores not motile. Though a sexual pro cess has not been observed, there are apparently male and female organs, autheridia and oogonia. The supposed male cells are set free and are not motile ; the supposed female cells are not set free. The sporangia and the sexual organs are borne on distinct indi viduals, and in some genera (e.g. , Dictyota, Taonia) the male and female organs are borne on distinct individuals. Order 5. Fucacete. Body multicellular ; generally differentiated into root and shoot ; shoot usually thalloid, cylindrical, or flattened, but differentiated into stem and leaves iu Sargassum. No asexual production of spores. Sexual organs antheridia or oogonia. Male cells numerous, set free, ciliated ; female cells (oospheres) either one (Pycnophycus, Himanthalia, Ci/stoseira, Sargassum}, two (Pelvctia), four ( Ozothallia], or eight (Fucus) in an oogonium, set free, not motile. The life-history of the PhsROphycese is in most cases imperfectly known. In the Fucaccee, since there is no asexual formation of spores, there is no alternation of generations, and there is no indi cation of any other kind of polymorphism. In those forms in which the sexual and asexual organs are restricted to separate indi viduals, as in Cladostephus (Sphacclaricx), in the Cutlcriacex, and in the Dictyotaccee, there may be an alternation of generations. In the Cutlcriaccse it is, in fact, highly probable. In the one genus, Zanardinia, the two generations are similar, differing only in the nature of their reproductive organs. In Cutlcria, the other genus, the two generations are dissimilar, the form known as Cut- Icria being the gametophyte, whereas the sporophyte appears to be a form which has been regarded as a distinct genus, under the name of Aglaozonia. In some genera of Dictyotaccaz (Taonia, Padina, Dictyopteris} there is a further indication of polymorphism, in that the spore (whether tetraspore or oospore) produces on germination a spherical or cylindrical protonematoid body, from which spring the shoots of the characteristic form. Since the life-history of the Ph&ophyccse. is so imperfectly known, the relations of the various orders cannot be accurately determined. The Diatomaccse and the Syngeneticfe are apparently isolated groups. The families of the Phseosporese form a series leading from the simple isogamous Ectocarpese through the Cutlcriaccx to the oogamous Fumccse. There are also points of resemblance in the vegetative parts between some of the Scytosiplioncve, and the Ijaminariess. Hub-Class IV. Rhodophycese. This sub-class includes the single order Floridcsc,. Order Floridcx. Multicellnlar plants ; body flattened or fila mentous ; when filamentous, either monosiphonous or polysiphon- ous, with or without a cortex ; thalloid, or with indications of differentiation into stem and leaf. Asexual reproduction, by means of uuciliated naked spores, which are usually tetraspores (wanting in Lcmanca], produced in unilocular sporangia. Sexual reproduc tion by means of male and female organs, termed antheridia and procarpia ; the procarpium is generally multicellular, but sometimes unicellular (Banyiaccee, Nemalicee), is always closed, and generally consists of two parts, the carpoyonium or sporogenous portion and the trichogyne or receptive portion. The male cells are non-motile and have a cell-wall (spermatia) ; there is no differentiated female cell in the procarpium. After fertilization the carpogenous cell (or cells) divides to form the mother-cells of spores, and each mother- cell gives rise to a single naked spore (carpospore), which is not ciliated and is usually non-motile ; in the Banyiaccas the carpo- spores exhibit amoeboid movements for a time. The group of sporo genous cells formed from the fertilized carpogenous cell (or cells) is termed a cystocarp ; in many cases these cells become surrounded by an investment developed, from the adjacent vegetative tissue. The structure of the cystocarp is very simple in the Bangiaccx, consisting only of eight spore mother-cells. The principal orders of the Floridcx are Banyiaccie, LcmancaceiE, Ncmalieie, Ccramiaccas, CorallinctK, Rhodomelaccas, CryptoncmioccK, Rhodymcniaccae, Wran- ycliaccx, Squamariaceee, Sphserococcaccas. With regard to the life-history of the FloridciK, it is generally considered to present a well-marked alternation of generations, the plant being the gametophyte, the fructification (cystocarp) formed in consequence of fertilization being the sporophyte. Further poly morphism has been detected in the genera Lcmanca and Eatracho- spcrmum. Here the carpospore does not at once give rise to the plant, but to a filamentous or flattened body, which in Batracho- spermum reproduces itself by spores, and from which the parent form springs as lateral branches. This filamentous form appears to be identical with species of the genus Chantransia ; it is therefore known as the Chantransia-form. Mutual Affinities and Phytogeny of Sub-Classes of Alg&. Comparison of the four sub -classes shows that, whereas the Chlurophycese and the Flixopliyccx present two fairly complete series of parallel forms, ranging from unicellular undifferentiated to multi- cellular more or less highly differentiated organisms, the Cyano- pliyccse, consist only of comparatively simple forms in which sexual reproduction is unknown, and the RJiodophyccee of comparatively complex forms in all of which a sexual process obtains. It has been suggested by Colin, Berthold, and others that there is a close re lation between the lowest Rhodophyccse (Bangia] and the higher filamentous Cyanophyccie (Scytoncmeie, Sirosiphoncse ), and that possibly the latter may have been derived from the former. On this view the Cyanopliycex and the Jl/todojj/iyceie, taken together, constitute a series which is on a level with those of the Chloro- phycex, and of the Phieophyccee. On comparing these three series together, it will be observed that they present a general correspond ence, in that the main types of form are to be found in all. Thus, the Chroococcaccee among the Cyanophyccw, the Palmellaceaz among the Chlorophyccas, and the Synyencticse, among the Phasophyccie are corresponding groups ; similarly, the Confervoidese among the Chloropnycc.se, correspond to the Ectocarpcse and oChe-r filament ous Phseophycese, and to various forms of Rhodophycc.se,, such as Bangia, Porphyra, Griffithsia, and Callithamnion ; and Chara (Chlorophyceae) resembles, at least in its vegetative structure, such forms as Cladostephus (Phieophyccse) and Polysiphonia (Rhodophy- CC<K). There are, however, forms belonging to some of the sub classes which have no representatives in others. Thus the orders Siphoncas, Volvocincaz, Hydrodictycse, belonging to the Chloro- jrfiyccx, are unrepresented in the other sub-classes, and this is true also of the Fucaccas and the Laminaricae, among the Pli&ophycciv. The Conjugate Ghlorophyccse, also form a peculiar group, the only corresponding forms being the Diatomoccae. (Phieophyceie), which present many points of resemblance to the Desmidiese. With regard to the phylogeny of the Alcjse, the possible derivation of the Rhodophyccie from the Cyanopkyccse, has already been pointed out. Assuming this, there are three series of Algse, closely allied in their origin, in each of which evolution has proceeded on more or less divergent lines, thus leading to the development of a number of corresponding forms in the three series. It is not impossible that the Chlorophyccse, and the Ph&opliyccee, may also have sprung from the Cyanophycese, not, like the Rhodophycese, from the higher forms, but from the lower. But, if the Cyanopliyccae, be regarded, not as primitive, but as degenerate, forms and for this view there are good grounds then the simpler Chlorophyccas are probably to be regarded as the forms from which the others have been derived. Literature of Alg x. Special papers referred to : Colin, Beitrcige zur Physiologic der Phycochromaceen, 1807; Berthold, "Die Bangiaceen," in Fauna und Flora des Goifes von Neapel, 1SS2; Zopf, Zur Morphologie der Spaltpflanzen, Leipsic, 1882 ; Hansgirg, Physiologische und Algologische Studien, Prague, 1887. Of general works consult Harvey, Phycologia Britannica ; Cooke, British Fresh water Algre, London, 1882 ; Thuret and Bornet, A otes Algologiques, i., ii., 1882-86, and Etudes Phycologiques, 1878; Palkenberg, "Algen," in Bchenk s Handbuch der Jlotanik, ii., Breslau, 1881-84; Hauck, "Die Meeresalgen," in Rabenhorst s Kryptogamen-P lora, 2d eel., Leipsic, 1885 ; Goehel, Outlines of Classification and Special Morphology, Oxford, 1880. These works contain refer ences to all the more important isolated papers on the Algce. CLASS II. FUNGI. In view of the description of these plants given in the article FUNGUS (q.v.), it is unnecessary to define them here further than as Thallophytes which are devoid of chlorophyll. The classification followed here differs in detail from that given in the previous article. It is as follows : Sub-Class I. Myxomycetes. ,, II. Schizomycetes. ,, III. Phycomycetes. a. Zygomycctcs. b. Oomycctcs. Order 1. Chytridiaccas. Order 1. Ancylistese. ,, 2. Mucorini. ,, 2. Peronosporeie. ,, 3. Entomophthorese. ,, 3. Saprolegniese. ,, 4. Ustilacjinciv. ,, IV. Ascomycetes. Order 1. Gymnoasccfe. Order 2. Pyrcnomycctcs. Order 3. Discomycctcs. ,, V. u^Ecidiomycetes. Order 1. Urcdincae. ,, VI. Basidiomycetes. Order 1. Trcmcllini. Order 2. Hymcnomycctcs. Order 3. Gastcromycctcs. The chief points of difference between this classification and that given in the article FUNUUS, besides the introduction of some addi tional orders, are the division of the Phycomycetes into Zygomycetes and Oomycctcs, the removal of the Ustilagineas from the Uredincx to the Phycomycetes, and the inclusion of the Erysiphess and Tuberaceie in the Pyrcnomycctcs, this order being considered as containing all the Ascomycetes which have well-developed, but more or less com pletely closed, apothecia (perithecia), in a word, all Ascomycetes which are neither GymnoascciK nor Discomycetes. The division of the Phycomycetes into Zygomycetes and Oomycctcs is necessary in order to distinguish those forms which are isogamous, and in which the sexual process is one of conjugation (see REPRODUCTION), from those which are oogamous, and in which the sexual process is one of fertilization, the former constituting the group Zygomycetes, the

latter the group Oomycctcs. The change in position of the Ustil-