256 THIRD GROUP. — VASCULAR CRYPTOGAMS. 



The growing point of the stem is shghtly convex and has, according to Holle, a long 

 one-sided apical cell ; a similar cell is found also in the smaller roots. According to 

 Schwendener ', a median section of a root of Marattia shows two apical cells lying 

 right and left of the median plane. From both these cells segments are cut off by 

 periclinal walls on the one hand for the root-cap, and on the other for the body of the 

 root ; longitudinal divisions also take place from time to time. A transverse section of 

 the rounded apex shows that altogether four such apical cells are grouped round the 

 centre''. 



II. EOUISETINEAE. 



A. HOMOSPOROUS EQUISETINEAE : EQUISETACEAE 

 (HORSE-TAILS) ^. 



Sexual generation or proihallhcvi (oophore, oophyle). The spores of the Equi- 

 setaceae, which retain their vitality only a few days, if sown in water or on moist 

 ground as soon as they are ripe show in a few hours the first preparations for 

 germination; in a few days' time the prothallium will have developed into a flat 

 pluricellular body, but its further growth will be slow. The spore, which contains a 

 nucleus and chlorophyll- corpuscles, increases in size as germination begins; it becomes 

 pear-shaped and bursts the exosporium, and divides into two cells, the smaller of 

 which has almost wholly colourless cell-contents and soon developes into a long 

 hyaline rhizoid (Fig. 209 /, //, /// w) ; the anterior and larger cell receives the 

 chlorophyll-corpuscles of the spore, which multiply by division, and it then produces 

 by further divisions the first lobe of the prothallium, which continues to grow at the 

 apex and soon branches (///, IV). The multiplication of the cells thus resulting 

 appears to, be very irregular ; the very first divisions vary ; sometimes the first wall in 



' Ueber Scheitelwachsthum mit mehreren Scheitelzellen (Sitzber. d. Ges. naturf Freunde in 

 Berlin, 1879). 



^ [See Bower, Morph. of the leaf in Vase. Crypt, and Gymnosp. (Phil. Trans. 1S84) for the 

 development of the leaf.] 



^ On the Calamites, vid. infra. G. W. Bischoff, Die kryptogamischen Gewachse, Nurnberg, 

 1828. — Hofmeister, Vergl. Unters. 1851 ; — Id. Ueber d. Keimung d. Equiseten (Abh. d. Kgl. Sachs. 

 Ges. d. Wiss. 1855, IV. 168) ; — Id. Ueber Sporenentwicklung d. Equiseten (Jahrb. f. wiss. Bot. III. 

 283). — Thuret in Ann. d. So. nat. 1851, XVI, 31.— Sanio, Ueber Epidermis u. Spaltoffn. d. Equis. 

 (Linnaea, Bd. 29, Heft 4). — C. Cramer, Langenwachsthum u. Gewebebildung bei Eqicis. arvense u. 

 sylvaticuin iPflanzenphys. Unters. von Nageli u. Cramer, III, 1S55). — Duval-Jouve, Histoire 

 naturelle de Equisetuiii, Yzxis, 1S64.— H. Schacht, Die Spermatozoiden im Pflanzenreich, Braunschweig, 

 1864. — Rees, Entwicklungsgesch. d. Stammspitze von Equiset. (Jahrb. f. wiss. Bot. 1867, VI. 209). — 

 Milde, Monographia Equisetorum in Nova Acta Acad. Leop. Carol, xxxv, 1867. — Nageli u. Leitgeb, 

 Entstehung u. Wachsthum d. Wurzeln. (Beitr. z. Wiss. Bot. von Nageli, Heft iv, Miinchen, 1867). — 

 Pfitzer, Ueber d. Schutzscheide (Jahrb. f. wiss. Bot. VI. 297). — Russow, Vergl. Unters. iiber d. Leit- 

 biindelkryptog., Petersburg, 1872, p. 41. — Janczewski, Ueber d. Archegonien (Bot. Ztg. 1872, p. 

 420). — Van Tieghem, Ueber Wurzeln (Ann. d. sc. nat. 5 ser. T. XIII). — Janczewski, Recherches 

 sur le developpement d. bourgeons dans les Preles (Mem. d. 1. soc. nat. d. sc. nat. de Cherbourg. T. 

 XX. 1876). — Famintzin, Ueber Knospenbildung bei Equiset. (Bulletin de I'Acad. d. Sc. de Peters- 

 bourg, p. xxii, 1876). — Sadebeck, Ueber Keimung u. Embryobildung in Schenk, Handb. d. Bot. i Bd. 

 pp. 174, 1S3, 221. — Goebel, Beitr. z. vergl. Entwickl.-Gesch. d. Sporangien (Bot. Ztg. 1880-1). — 

 On Spermatozoids, see Strasburger in d. Jen. Zeitschr. Bd. X. p. 401 ff., and Zellbildungu. Zelltheilung, 

 III Ed. p. 96; also Sadebeck, Die Entw. d. Keimes d. Schachtelhalme ;Pringsheim's Jahrb. Bd. XI, 

 und Encykl. d. Nat. Wiss. Bd. I).- 



