TRIMITIA. 



[ 087 ] rPJMORDIAL UTRICLE. 



I of this strenpftli is sufficient for freneral 

 use. The same may be applied to insects 

 in the cabinet, by means of a hair-pencil. 

 Bn-keley points out that carbolic acid alters 

 the colour of some fungi. 



RiBL. Treatise upon the INIicroscope 

 (liVTROD.) ; Corti, Sieb. und Kiill. Zeit. iii. 

 1.34 ; Goadby, Amer. J. xiii. 15 ; Davies- 

 Matthews, Mounting ; Mohl, Bot. Zeit. xv. 

 249 ; Beale, IIoio ; Carpenter, Microscope ; 

 Fray, Mikr. ; Strieker, Hid. ; Heys and 

 Hepworth, Tr. Mic. Sac. 186-5 ; Lawrence, 

 Qu. Mic. Jn. 1859, 257; Walmsley, Mn. 

 Mic. Jn. i. 380; Bastian, ibid. i. 94; 

 Mouchet, ibid. iii. 7o ; B.ichmann, Anf. mik. 

 Praparat. 



PRDII'TIA, .T. & H.— A small fossil 

 Ostracode with suboblong valves, impressed 

 with a varialile furrow or pit in the medio- 

 dorsal region. Forty species in the Silurian 

 rocks of Britain, Europe, and America. 



BiBL. Jones & Hall, Ann. N. H. 3. xvi. 

 415. 



PRIMORDIAL UTRICLE.— This term 

 indicates a peculiar portion of the contents 

 of the cellulose sac constituting a vegetable 

 cell. As the formations comprehended 

 under this name are of great importance in 

 the development of vegetable cells, a little 

 detail must be entered into in explaining 

 the subject. 



If a cell of the pulp of any succulent 

 fruit, a cell of yeast, or cells in sections 

 taken fi-om the delicate nascent tissues of 

 any growing part of plants, are placed in 

 water, the entire contents will soon be seen 

 to retract from the cellulose wall, leaving a 

 clear space, filled with transparent liquid, 

 between the latter and a sharply detiued 

 line bounding the contracted or coagulated 

 contents (PL 47. figs. 1, 2, 10-12). The 

 addition of tincture of iodine makes the 

 conditions still more clear. If the parent 

 cells of pollen-grains or spores are treated 

 thus, just before the development of the 

 cellulose wall of the special parent cells (see 

 Pollen), the four portions of the contents 

 of the parent cell contract and separate, and 

 each portion, containing its own granular 

 stnictures and nucleus, appears bounded by 

 a well-defined line (fig. 607). This well- 

 defined line presents in this condition the 

 appearance of a delicate membrane or pel- 

 licle enclosing the entire contents. The 

 action of acids, or spirit, and iodine, reveals 

 the existence of a similar set of conditions 

 in all actively vegetating cells ; and in most 

 cases a more or less thick viscous layer of 



the protoplasm is found lining the cellulose 

 wall before the application of the reiigents. 

 Since the line indicating the boundary of 

 the contents cannot be distinctly seen until 

 the contents have retracted from the cellu- 

 lose wall, and since the protoplasm is always 

 coagulated by the action of the reagents, it 



Fig. 607. 



Fig. 608. 



CM-...i 



Fig. 607. Parent celJa of pollen-grains jnst after the 

 separation of the contents into four portions, treated 

 with iodine. CM, the parent cell. P, the protoplasmic 

 portions, each with a nucleus and a well-defined outline 

 at the surface of the primordial utricle. Magnified 250 

 diameters. 



Fig. 608. Cells of Protococcus multiplying. The green 

 granular contents are bounded by the definite outline 

 of the primordial utricle : the primary and secondary 

 cellulose parent-cell membranes are represented as 

 separated from each other. Magnified 400 diameters. 



is a subject of discussion whether the film 

 forming the well-defined line on the surface 

 of the contracted contents is a true struc- 

 ture, or_ only a pellicle produced by the 

 coagulation of the surface of the protoplasm, 

 just as a "skin" forms over size, or other 

 similar substances when they dry up in the 

 air. ■\'ery young cells often appear tiUed 

 with a dense protoplasm (young autheridial 

 cells of Cryptogamia, embryo-sacs of many 

 flowering plants, cells about to produce 

 zoospores in the Confervoids, &c.), which 

 may produce numerous new cells by merely 

 breaking up into separate portions; and 

 thus the fvmction of the primordial utricle 

 is shared by the entire mass of contents. 

 Young cells of nascent tissues, presenting 

 this condition at first, acquire the primor- 

 dial utricle afterwards, simply by the dense 

 contents becoming excavated as the cell- 

 wall expands, and following this in its 

 growth, so that the originally dense homo- 

 geneous mass becomes a hollow sphere 

 with the centre occupied by watery cell- 

 sap; in other cases the originally homo- 

 geneous protoplasm becomes excavated by 

 nimierous water-vesicles, and thus honey- 

 combed, until it forms a mere reticulation 

 of protoplasmic threads upon the wall or 

 stretched across the cavity. The proto- 

 plasmic layer lying upon the wall of the 



