Text-book of botany : morphological and physiological / by Julius Sachs ; translated and annotated by Alfred W. Bennett ; assisted by W.T. Thiselton Dyer.

Date:
1875
Catalogue details

Licence: Public Domain Mark

Credit: Text-book of botany : morphological and physiological / by Julius Sachs ; translated and annotated by Alfred W. Bennett ; assisted by W.T. Thiselton Dyer. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    coalescing1; and even in these cases they probably differ internally, since it is diffi- cult to explain on any other hypothesis the necessity for their union into a product capable of development (the Zygospore). In some other Conjugate, as Spirogyra, this internal differentiation is exhibited at least to the extent that the contents of one of the conjugating cells pass over into the other which remains stationary. But usually, even in many Algae (as Vaucheria, (Edogonium, Coleochaste, Fucus, &c.) and Fungi (Saprolegnia), and in all Characeae, Muscinese, Vascular Cryptogams, and Phanerogams, a great variety of differences are manifested between the sexual cells as to size, form, motility, mode of production, and the share they take in the form- ation of the product of the union. This differentiation presents, especially in the Algae and Fungi, a most complete series of gradations between the conjugation of similar cells and the fertilisation of the oosphere by antherozoids, any boundary line between these two processes being unnatural and artificial. The difference also between the sexual cells is developed only gradually and step by step, like the ex- ternal and internal differentiation of plants; and it is this that renders it probable that in the lowest forms of the vegetable kingdom, as in the Nostocacese, no process at all of this kind exists, or that at all events there are plants of extremely simple structure in which no such process occurs. Wherever there is an evident external difference between the two sexual cells, one behaves actively in the union, and loses in the process its individual existence, the other behaves passively, absorbing into itself the substance of the active one, and furnishing by far the larger proportion of the first materials for the formation of the immediate product of the union. The former is termed the male or sperm-cell, the latter the female or germ-cell or oosphere. These most essential features of the sexual process may also be recognised in the fertilisation of the Ascomycetes and Florideae, although the external appearance of the sexual organs, the ascogonium and trichophore on the one hand and the antheridia on the other hand, are strikingly different from those which occur in any other class of plants2 3. The usual condition of the female cell during the 'sexual process (except in the Ascomycetes and Florideae) is that of a naked primordial cell (oosphere), formed either by simple contraction of the protoplasm of a cell previously enclosed within a cell-wall (the oogonium of Vaucheria, (Edogonium, and Coleochsete, the central cell of the archegonium of Muscineae and Vascular Cryptogams) or by the division of the protoplasm of a mother-cell combined with contraction and rounding off of the daughter-cells (as in Saprolegnia and Fucaceae), or by free-cell-formation (as in the corpusculum of Coniferae ? and the embryo-sac of Angiosperms). In all these cases the germ-cell is spherical or ellipsoidal, except that in the Angiosperms it is some- times elongated; in general its form is the simplest that the vegetable cell can assume. The rounding off is not connected with any internal differentiation; at 1 See De Bary, Die Familie der Conjugaten, Leipzig 1858, p. 57; Pringsheim, Monatsber. der Berlin. Akad. Oct. 1869, Paarung der Schwarmsporen [Ann. des sci. nat. 5th series, 1869, vol. XII, pp. 191 and 211 ; De Bary, ibid, p.208]; Pfitzer, in Hanstein’s Botanische Abhandlungen, 1871, Heft II, p. 70 et seq. 3 De Bary, Beitriige zur Morphologie und Physiologie der Pilze, Frankfort, Heft III, at the end.