pit-threads and wall-threads may occur in the same cell, but more often the threads are limited to the pits. The pit-threads are larger and stain more readily than the wall-threads. The threads vary in size in different plants. They are very thick in Viscum album, and are well seen in Phaseolus multiflorus and Lilium Martagon. They are present from the beginning of the development of the cell-wall, and arise from the spindle fibres, all of which may be continued as connecting threads (endosperm of Tamus communis), or part of them may be overlaid by cellulose lamellae (endosperm of Lilium Martagon), or they may be all overlaid as in pollen mother-cells and pollen grains of Helleborus foetidus. The presence of these threads between all the cells of the plant shows that the plant body must be regarded as a connected whole; the threads themselves probably play an important part in the growth of the cell-wall, the conduction of food and water, the process of secretion and the transmission of impulses.
Literature.—The following is a list of a few of the more important papers in which further information and a more complete list of literature will be found: Allen, "Nuclear Division in the Pollen Mother-cells of Lilium canadense," Annals of Botany (1905), vol. xix.; Berghs, "La Formation des chromosomes hétérotypiques dans la sporogénèse végétale," La Cellule (1904), vol. xxi.; Blackman, "On the Fertilization, Alternation of Generations, and General Cytology of the Uredineae," Ann. of Bot. (1904), vol. xviii.; Bütschli, Untersuchungen über mikroskopische Schäume und das Protoplasma (Leipzig, 1892; Eng. trans. by Minchin, London, 1894); also Untersuchungen über Struktur (Leipzig, 1898); Courchet, "Recherches sur les Chromoleucites," Ann. d. sci. nat. (bot.): (1888); Delage, L'Année biologique: comptes rendus annuels des travaux de biologie générale (Paris, 1895), &c.; Farmer, "Recent Advances in Vegetable Cytology," Science Progress (1896), vol. v.; "The Cell and some of its Constituent Structures," Science Progress (1897); Farmer and Moore, "On the Meiotic Phase in Animals and Plants," Quart. Journ. Micr. Sci. (1905), vol. xlviii.; Farmer and Digby, "Studies in Apospory and Apogamy in Ferns," Ann. of Bot. (1907), vol. xxi.; "On the Cytological Features exhibited by certain Varietal and Hybrid Ferns," Ann. of Bot. (1910), vol. xxiv.; Fischer, Fixirung, Färbung und Bau des Protoplasmas (Jena, 1899); Flemming, "Morphologie der Zelle," Ergebnisse der Anatomie und Entwickelungsgeschichte (1896); Gardiner. "The Histology of the Cell-Wall, with Special Reference to the Mode of Connexion of Cells," Proc. Roy. Soc. (1897-1898), lxii., and his earlier papers there cited; see also Proc. Camb. Phil. Soc. (1908), vol. ix.; "The Genesis and Development of the Wall and Connecting Threads in the Plant Cell. Preliminary Communication," Proc. Roy. Soc. (1900), lxvi.; Gates, "A Study of Reduction in Oenothera rubrinervis," Bot. Gaz. (1908), vol. xlvi.; Green, "The Cell Membrane," Science Progress (1897), new series, vol. i.; Grégoire, "Les Cinèses polliniques chez les Lilicacées," La Cellule (1899), vol. xvi.; "Les Résultats acquis sur les cinéses de maturation dans les deux régnes," La Cellule (1905), vol. xxii. and (1910) vol. xxvi.; Grégoire and Wygaerts, "La Reconstitution du noyau et la formation des chromosomes dans les cinèses somatiques," i. La Cellule (1903), vol. xxi.; Guignard, "Sur les anthérozoides et la double copulation sexuelle chez les végétaux angiospermes," Comptes rendus (1899), 128; Haberlandt, Physiologische Pflanzenanatomie (Leipzig, 1909); Die Lichtsinnesorgane der Laubblätter (Leipzig, 1905); R. A. Harper, Sexual Reproduction and the Organisation of the Nucleus in certain Mildews (pub. Carnegie Institution, 1905); M. Hartog, "The Dual Force of the Dividing Cell," Proc. Roy. Soc., B. lxxvi.; Henneguy, Leçons sur la cellule, morphologie et reproduction (Paris, 1896); O. Hertwig, Die Zelle und die Gewebe (Jena, 1893 and 1898; see Eng. ed., London, 1894); Hirase, "Études sur la fécondation et l'Embryogénie du Ginkgo biloba," Journ. Coll. Sci. Imp. Univ. (Japan, 1895); Ikeno, "Untersuchungen über die Entwickelung der Geschlechtsorgane und den Vorgang der Befruchtung bei Cycas revoluta," Jahr. f wiss. Botanik (1898), 32; Lee, The Microtomist's Vade Mecum (London, 1900); Macallum, "On the Detection and Localization of Phosphorus in Animal and Vegetable Cells," Proc. Roy. Soc. (1898), vol. lxiii.; "On the Distribution of Assimilated Iron Compounds other than Haemoglobin and Haematins, in Animal and Vegetable Cells," Quart. Journ. Micr. Sci. (1896), vol. xxxviii.; Meyer, Untersuchungen über die Stärke-Körner (Jena, 1895); Montgomery, "Comparative Cytological Studies, with especial regard to the Morphology of the Nucleolus," Journ. of Morphology, vol. xv. (Boston, 1899); D. M. Mottier, "The Development of the Heterotype Chromosomes in Pollen Mother-cells," Ann. of Bot. (1907), vol. xxi.; "On the Prophases of the Heterotype Mitosis in the Embryo-sac Mother-cell of Lilium," Ann. of Bot (1909), vol. xxiii.; Fecundation in Plants (Carnegie Institution, 1904}: Nawaschin, "Resultate einer Revision der Befruchtungsvorgänge bei Lilium Martagon und Fritillaria tenella," Bull. de l'acad. des sci. de St Petersbourg (1898); "Ueber die Befruchtungsvorgänge bei einigen Dicotyledoneen," Ber. d. deutsch. bot. Gesell. (1900}, vol. 18; Rosenberg, "Cytologische and morphologische Studien an Drosera longifolia X. rotundifolia," Kungl. svenska vetenskapsakad. handl. (1909), vol. xliv.; Salter, "Zur näheren Kenntniss der Stärkekörner," Pringsh. Jahrb. (1898); Sargant, "The Formation of the Sexual Nuclei in Lilium Martagon, I. and II.," Ann. of Bot. (1896-1897), vols. x. and xi.; "Recent Work on the Results of Fertilization in Angiosperms," Ann. of Bot. (1900), vol. xiv.; Schimper, "Sur l'Amidon et les Leucites," Ann. des sci. nat. (bot.) (1887); Scott, "Development of Articulated Laticiferous Vessels," Quart. Journ. Micr. Sci. (1882); "On the Laticiferous Tissue of Manihot Glaziovii (the Cearà Rubber)," Quart. Journ. Micr. Sci. (1884); Strasburger, "Chromosomenzahlen, Plasmastrukturen, Vererbungsträger und Reduktionsteilung," Jahrb. wiss. Bot. (1908), vol. xlv.; Histologische Beiträge vols. i. to vii. (Jena); Strasburger and others, "Cytologische Studien aus dem Bonner botanischen Institut," Jahrb. für wissensch. Botanik (1897), vol. 30; Wager, "On Nuclear Division in the Hymenomycetes," Ann. of Bot. (1893), vol. vii.; "On the Structure and Reproduction of Cystopus candidus," Ann. of Bot. (1896), vol. x.; "The Cell Structure of the Cyanophyceae," Proc. Roy. Soc. (1903), vol. lxxii.; Wager and Peniston, "Cytological Observations on the Yeast Plant," Ann. of Bot. (1910), vol. xxiv.; Webber, "The Development of the Antherozoids of Zamia," Bot. Gaz. (1897), vol. xxiv.; Wilson, The Cell in Development and Inheritance (New York and London, 1900); Zimmermann, "Sammel-Referate aus dem Gesammtgebiete der Zellenlehre," Beihefte zum bot. Centralbl. (1893 and 1894); Die Morphologie und Physiologie des pflanzlichen Zellkernes (Jena, 1898). (H. W.*)
Morphology of Plants
The term morphology, which was introduced into science by Goethe (1817), designates, in the first place, the study of the form and composition of the body and of the parts of which the body may consist; secondly, the relations of the parts of the same body; thirdly, the comparison of the bodies or parts of the bodies of plants of different kinds; fourthly, the study of the development of the body and of its parts (ontogeny); fifthly, the investigation of the historical origin and descent of the body and its parts (phylogeny); and, lastly, the consideration of the relation of the parts of the body to their various functions, a study that is known as organography.
It is this last department of morphology that was the first to be pursued. The earliest scientific result of the study of plants was the recognition of the fact that the various parts of the body are associated with the performance of different kinds of physiological work; that they are, in fact, organs discharging special functions. The origin of the organography of the present day may be traced back to Aristotle, who described the parts of plants as "organs, though very simple ones." It was not until many centuries had passed that the parts began to be regarded from the point of view of their essential nature and of their mutual relations; that is, morphologically instead of organographically. Joachim Jung, in his Isagoge phytoscopica (1678), recognized that the plant-body consists of certain definite members, root, stem and leaf, and defined them by their different form and by their mutual relations. This point of view was further developed in the following century by Caspar Friedrich Wolff (Theoria generationis, 1759), who first followed the development of the members at the growing-point of the stem. He observed that the "appendicular organs," as he called the leaves, are developed in the same way, whether they be foliage-leaves, or parts of the flower, and stated his conclusions thus: "In the entire plant, whose parts we wonder at as being, at the first glance, so extraordinarily diverse, I finally perceive and recognize nothing beyond leaves and stem (for the root may be regarded as a stem). Consequently all parts of the plant, except the stem, are modified leaves." Similar views were arrived at by Goethe, though by the deductive rather than the inductive method, and were propounded in his famous pamphlet, Versuch die Metamorphose der Pflanzen zu erklären (1790), from which the following is a quotation: "The underlying relationship between the various external parts of the plant, such as the leaves, the calyx, the corolla, the stamens, which develop one after the other and, as it were, out of one another, has long been generally recognized by investigators, and has in fact been specially studied, and the operation by which one and the same organ presents itself to us in various forms has been termed Metamorphosis of Plants."
Pure Morphology.—Thus it became apparent that the many
