LFCOPOD1NEAE. PSILOTACEAE. 283 



a vascular bundle. Branching appears to be rare, at all events much rarer than 

 in Psilotum. 



The position of the sporangia is peculiar. They are sunk in the apex of short 

 branches bearing two leaves, and in Psilotum apparently they form a single sporan- 

 gium with three (two to four) compartments, in Tmesipteris one of two compartments. 

 The small spikes of sporangia are formed at the growing point of the primary 

 shoot in the same way as the branches. Then two distinct rudiments of leaves arise 

 beneath the summit of the young sporangiferous spike. By more rapid growth of the 

 tissue of the sporangiferous shoot at the point of insertion of the leaves they are carried 

 up on a common base, and then appear to form a single two-cleft leaf. The sporangia 

 are sunk in the expanded summit of the branchlet and their development agrees with 

 that of the sporangia of the other Eusporangiatae ; they form in Psiloium usually 

 three, sometimes two or four compartments separated by longitudinal walls (composed 

 of a few layers of cells) and an axile mass of tissue ; the compartments are strongly 

 protuberant outwards. A vascular bundle is formed in the fertile branch and 

 terminates beneath the sporangia. The portion of the branch beneath the sporangia 

 is usually very short, and has therefore been sometimes incorrectly described as the 

 ' stalk ' of the trilocular sporangium which arises on the base of the two-cleft leaf. 

 That this view is incorrect is shown by the history of development and by the fact that 

 the fertile branches are sometimes more than a centimetre in length and have all the 

 characters of the sterile branches (Goebel, loc. cit.\ Upon the ripe sporangia is an 

 indentation running lengthwise, where they subsequently open by a longitudinal 

 fissure. In Tmesipteris the sporangiferous spikes have as a rule only two sporangia, 

 one of which is turned towards the primary axis, the other away from it. 



Psilotum has a cauline bundle \ which is circular in the transverse section in the aerial 

 branches and is separated by an endodermis from the surrounding parenchyma ; the 

 vascular portion is composed of from three to eight groups of vessels ; in the centre of 

 the bundle are threads of sclerenchyma, and between the groups of vessels is 

 parenchymatous tissue, in which, especially towards the circumference, groups of a few 

 narrower sieve-tubes with thicker walls lie scattered here and there. 



C. THE LIGULATAE 2 . 



The two last groups of the Lycopodineae, the Selaginelleae and Isoeteae, 

 together make up the Ligulatae. Both have two kinds of spores, large female 

 macrospores and small male microspores. 



1 De Bary, Vergl. Anatomic, p. 362. 



2 Hofmeister, Vergl. Untersuch. 1851 ; Id. Entw. von Isoetes lacustris (Abhandl. d. Kon. Sachs 

 Ges. d. Wiss. iv, 1858). Nageli u. Leitgeb, Ueber Entstehung u. Wachsth. d. Wurzeln in Nageli's 

 Beitr. z. wiss. Bot. iv, 1867. A. Braun, Ueber Isoetes (Monatsber. d. Berliner Akad. 1863). Milde, 

 Filices Europae et Atlantidis, Leipzig, 1867. Millardet, Le prothallium male des crypt, vase. 

 Strasburg, 1869. Pfeffer, Entw. d. Keims der Gattung Selaginella in Hanstein's bot. Abhandl. iv, 

 1871. Janczewskiin Bot. Ztg. 1872, p. 441. Tschistiakoff, Ueber Sporenentw. von Isoetes (Nuovo 

 giornaleBot. Ital. 1873, p. 207). Russow, Vergl. Unters. Petersburg, 1872, p. 134 ff. Goebel, Beitr. 

 z. vergl. Entw.-Gesch. d. Sporangien (Bot. Ztg. 1880 u. 1881). De Bary, Vergl. Anat. Isoetes, 

 PP- 2 9 T > 361, 641. Bruckmann, Ueber Anlage u. Wachs. d. Wurzeln von Lycopodium und Isoetes 

 (Jen. Zeitschr. f. Naturw. viii, 522). Kienitz-Gerloff, Entw. d. Embryos von Isoetes lacustris (Bot. Ztg. 

 1881). Treub, Recherches sur les organes dela vegetation du Selaginella Martensii (Musee bot. de 

 Leide II). Hegelmaier, Zur Kenntn. einiger Lycopodinen (Bot. Ztg. 1874). [Belajeff, Antheridien 

 u. Spermatozoiden d. heterosporen Lycopodiaceen (Bot. Ztg. 1885).] 



