46g 
among the Dichotomeae in that they possess spores of two kinds, the macrospores 
and the microspores. As in the Rhizocarpese so here the carrying back of sexual 
differentiation to the development of the spores is associated with this peculiarity, 
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 
FJG, 32g. — Germination of the microspores oi 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, ß ß its ventral cells, 
C and D the formation of the antherozoids, ß and S have disappeared : v is the vegetative cell (prothallium of Millardet) ; 
a—f development of the antherozoids (A^D and a—d X 580, e and / 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 iv), 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 ^ 
Nägeli's Beitr. z. Wiss. Bot, IV. 1867. — A. Braun, über ZsoeV^s, in Monatsber. d. Berl. Akad. 1863. — ■ 
Milde, Filices Europae 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, über 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 Selaginella Martensii, 1877.] 
