FILICINEM, 



46g 



among the Dichotomeae in that they possess spores of two kinds, the macrospores 

 and the microspores. As in the Rhizocarpeae so here the carrying back of sexual 

 differentiation to the development of the spores is associated with this pecuHarity, 

 that the spores in germinating seem to attain their object, the formation of re- 

 productive organs, as directly as possible, for the prothallium is not a plant capable 

 of independent growth but a development of tissue within the spore. The mode 

 in which this is brought about in the Ligulatae differs in essential points from 

 that obtaining among the Rhizocarpeae. 



The Microspores of Isoetes and Selaginella do not produce the mother-cells of 

 the antherozoids immediately from their contents, as was formerly thought. To the 

 treatise of Millardet mentioned in the foot-note we owe our knowledge of the fact, 

 so important in connection with the relationship of the higher Cryptogams to the 

 Gymnosperms, that at the period when the microspores are ripe, their contents are 

 transformed into a mass of tissue consisting of but few cells. One of these cells 



Fig. 329. — Germination of the microspores of Isoetes lacustris (after Millardet). A and C microspores seen on the right 

 side, B and D on the ventral face ; A and B show the formation of the antheridium, S S its dorsal cells, ^ fi its ventral cells, 

 C and D the formation of the antherozoids, /S and S have disappeared : v is the vegetative cell (prothallium of Millardet) ; 

 «— ^/"development of the antherozoids (A-^D and a—d X 580, e andy X 700). 



remains sterile, and may be considered a rudimentary prothallium ; while from the 

 others originate the mother- cells of the antherozoids, and these may therefore be 

 looked on as a rudimentary antheridium. 



The microspore of Isoetes lacustris breaks up, after hibernation, into a very 

 small sterile cell and a large one comprising the whole of the rest of the contents 

 (Fig. 329 A — C). The former {v\ cut off by a firm wall of cellulose, does not 

 undergo any further considerable changes ; the latter, on the other hand, splits up 

 into four primordial cells without cell-walls, of which the two ventral ones produce 



Nageli's Beitr. z. Wiss. Bot. IV. 1867. — A. Braun, iiber /soeV^s, in Monatsber. d. Berl. Akad. 1863. — • 

 Milde, Filices Europse et Atlantidis, Leipzig 1867.— Millardet, le prothallium male des crypt, vase. 

 Strasburg 1869.— Pfeffer, Entw. des Keims der Gattung Selaginella in Hanstein's Bot. Abhand. IV. 

 1871.— Janczewski, Bot. Zeitg. 1872, p. 441. — Tschistiakoff, liber Sporenentwickelung von Isoetes, in 

 Nuovo Giornale bot. Ital. 1873.— Russow, Vergl. Unters. Petersburg 1872.— [Braun, Ueb. Blatt- 

 stellung und Verzweigung bei Selaginella, Sitzber. d. bot. Ver. d. Prov. Brandenburg, 1874. — Hegel- 

 maier, Zur Kennt. einiger Lycopodinen, Bot. Zeitg. 1874. — Treub, Recherches sur les organes de la 

 vegetation du Sdaginella Martensii, 1877.] 



