36- 



VASCULAR CRVPTOGAMS. 



CLASS VII. 



EQUISETACE^^ 



The Sexual Generation or Prothallium. The spores of the Equisetaceae which 

 have just attamed the ripe condition (they retain their power of germination only 

 for a few days), show, when sown in water or on damp soil, the preparatory 

 phases of germination after only a few hours. In the course of some days the 

 prothallium becomes developed into a multicellular plate, the further growth of 

 which then proceeds very slowly. The spore, which contains a nucleus and grains 

 of chlorophyll, increases in size as soon as germination commences, becomes 

 pear-shaped, and divides into two cells, one of which is smaller with scarcely 

 any except colourless contents, and soon developes into a long hyaline root-hair 

 (Fig. 269, /, //, ///, w), while the anterior and larger cell includes all the chloro- 

 phyll-grains of the spore which multiply by division. This cell produces by 

 further divisions the prtmary plate of the prothallium, which increases by apical 

 growth and soon branches {III- VI). The process of multiplication of the cells 

 is therefore apparently extremely irregular; even the very first divisions vary; 

 sometimes the first wall in the primary apical cell which contains chlorophyll is 

 but little inclined with respect to the longitudinal axis of the young plant (in E. Tel- 

 viaicia the axis sometimes dichotomises) ; in other cases, on the contrary, this cell 

 developes into a longish tube, the apical part of which is cut off by a septum (occa- 

 sionally in E. arvense). The further growth is brought about by one or more apical 

 cells dividing by septa, and longitudinal walls are subsequently formed in the seg- 

 ments in an order very difficult to determine. Ramification takes place by the 

 bulging out of lateral cells, which then continue their growth in a similar manner. 

 The chlorophyll-grains increase simultaneously by division in the cells. The young 



^ G. W. Bischoff, Die kryptogamischen Gewachse (NiiiTibeig 1828). — W. Hofmeister, Vergl. 

 Unters. (185 1). — Ditto, Ueber die Keimung der Equiseten (Abh. der konigl. Slchs. Gesell, d. Wiss. 

 1855, vol. IV. p. 168). — Ditto, Ueber Sporenentwickelung der Equiseten (Jahrb. fiir wiss. Bot. vol. III. 

 p. 283). — [Germination, Development, and Fructification of the Higher Cryptogamia (Ray Society), 

 pp. 267-306]. — Thuret (in Ann. des Sci. Nat. 1851, vol. XVI. p. 31). — Sanio, Ueber Epidermis 

 und Spaltoffnungen des Equis. (Linngea, vol. XXIX. Heft 4). — C. Cramer, L'ingenwachsthum und 

 Gewebebildung bei E. arvense und sylvaticum (Pflanzenphys. Unters. von Niigeli und Cramer, 1855, 

 vol. III.). — Duval- Jouve, Hist. Nat. des Equisetum (Paris 1864). — H. Schacht, Die Spermatozoiden 

 im Pflanzenreich (Braunschweig 1864). — Max Rees, Entwickelungsgeschichte der Stammspitze von 

 Equisetum (Jahrb. fiir wiss. Bot. 1867, vol. VI. p. 209). — Milde, Monographia Equisetorum, in Nova 

 Acta Acad. Leop. Carolina, 1867, vol. XXXV. — N^geli und Leitgeb, Entstehung und Wachsthum 

 der Wurzeln (Beitr. zur. wissen. Bot. von Nageli, Heft IV. Munchen 1867). — Pfitzer, Ueber die 

 Schutzscheide (Jahrb. fiir wissen. Bot. vol. VI. p. 297). 



