PROEMBRYO. 



[ 538 ] 



PROTOCOCCUS. 



these, as will be noticed under that head and 

 under Spiral Structures. 



The protoplasmic substances indistin- 

 guishably connected with the so-called pri- 

 mordial utricle, are also the active agents in 

 the Rotation or circulation of the cell- 

 contents. Further relations of these nitro- 

 genous matters are also dwelt upon under 

 Chlorophyll and Starch. 



BiBL. Von Mohl, Botan. Zeit. ii. p. 273. 

 (1844), transl. in Taylor's Scient. Mem. iv, p. 

 91, Vermischte Schrift. p. 362; Henfrey, Ann. 

 N. H. xviii. p. 364; Nageli, Zeitschr.f. Wiss. 

 Bot. heft 1 (1844), & 3, 4 (18^6), transl. in 

 Ray Soc. Vols. 1845. p. 215 & 1849. p. 94 ; 

 Alex. Braun, Verjungung, Sfc. (trans, in Hay 

 Soc. Vol. 1853. p. 121 et seq.); Cohn, Nova 

 Acta, xxii. p. 605, transl. in Ray Soc. Vol. 

 1853. p. 517 ; Pringsheim, Bau. u. Bild. d. 

 Pjlanzenzelle, heft 1. Berlin, 1854; Hartig, 

 Bot. Zeitung, xiii. p. 393 et seq. 1855 ; 

 Criiger, ibid. p. 601; Mohl, ihid. p. 689. 



PROEMBRYO.— The term applied to 

 the structure first produced from the ger- 

 minal vesicle of Flowering Plants, after im- 

 pregnation, consisting of the suspensor and 

 the embryonal cell at its extremity. The 

 proerabryos of the Gymnosperms are espe- 

 cially remarkable (see Ovule). The same 

 term is often incorrectly applied to the pro- 

 thallium, the cellular structure first pro- 

 duced in the germination of the spores of 

 the higher Flowerless Plants. In the 

 Mosses this is a Confervoid expansion 

 (fig. 482. page 434), upon which buds are 

 formed from which arise the leafy stems ; 

 in the Ferns the prothallium (figs. 240-3, 

 page 262) is a MarcJiantia-Wke body, upon 

 wdiich are developed archegonia and anther- 

 idia; in the Lycopodiace^ and Marsi- 

 leace^ (figs. 581, 582, p. 507) the prothal- 

 lium is produced within the coats of the 

 ovule- spore. 



BiBL. See the heads referred to. 



PROROCENTRUM, Ehr.— A genus of 

 Infusoria, of the family Cryptomonadina. 



Char. Eye-spot absent; carapace smooth, 

 terminating in a point or tooth in front ; a 

 single flagelliform filament present. Marine. 



P. micans (PI. 24. figs. 70 & 71). Ovate, 

 compressed, attenuate behind, dilated in 

 front. Length 1-430". Luminous. 



P. viride. 



BiBL. Ehrenberg, Infus. p. 44; Ber. d. 

 Berl. Akad. 1840. 201. 



PRORODON, Ehr.— A genus of Infu- 

 soria, of the family Enchelia. 



Char. Body covered with vibratile cilia, 



truncate in front ; mouth with a cylinder of 

 teeth. Aquatic. 



P. teres (PI. 24. fig. 72). Body ovate, 

 terete, white. Length 1-140". 



Two other species, one of them green. 



Dujardin places this genus in tlie family 

 Paramecina. 



BiBL. Ehrenberg, Jw/i<5. p. 315, and Ber. 

 d. Berlin Akad. 1840. 201. 



PROSENCHYMA. See Tissues, ve- 

 getable. 



PROSTHEMIUM, Kunze.-A genus of 



Fig. 614. 



Prosthenium betulinum. 



Spores and paraphyses seen in a vertical section of fruit. 



Magnified 200 diameters. 



Sphaeronemei (Coniomycetous Fungi), grow- 

 ing upon the branches of trees, forming 

 circular depressed spots; the perithecia 

 enclose erect articulated filaments bearing 

 radiating tufts of two or three septate spores 

 (fig. 614), P. betulinum occurs upon the 

 bark of the branches of the birch-tree. 



BiBL. Berkeley, Brit. Flor. ii.pt. 2. p. 297. 



PROTEACE.E.— A family of Dicotyle- 

 donous plants, mostly from New Holland or 

 the Cape, shrubs or small trees {Banksia, 

 Grevillea, Hakea, &c.), of remarkable rigid, 

 evergreen habit. The coriaceous leaves are 

 well suited for the study of the epidermal 

 structures, and the stomates have interesting 

 peculiarities (see Stomata). The epidermis 

 is often scurfy with scattered hairs, some of 

 which are of curious forms (PI. 21. fig. 29). 



PROTEUS.— An old name applied to 

 certain Infusoria, as Amoeba, &c. 



PROTHALLIUM. See Proembryo. 



PROTOCOCCUS, Ag.— A genus of Pal- 

 mellacese (Confervoid Algae), at present very 

 imperfectly known, since without a tolerably 

 complete history of the development of the 

 forms it is impossible to distinguish the tme 

 species of Protococcus from the young states 

 of the more complicated Palmellaceaj, and 

 even from the germinating gonidia of the 

 Lichens. As we have limited it, Protococcus 



