l8 9i] Current Literature. 239 



tative organs is peculiar. The roots of these plants show in several 

 species a function, corresponding to that of a rhizome, and have 

 hitherto often been considered as identical with a " thallus " or a 

 "stem." They are always dorsiventral and often strongly flattened; 

 one genus, Tristicha, is, however, according to Cario evidently desti- 

 tute of any kind of roots. As to the internal structure of the roots, 

 there is neither any endodermis nor pericycle, but the central-cylinder 

 is surrounded by a collenchymatic tissue, which is especially strongly 

 developed on the dorsal face; the groups of leptome occupy the 

 dorsal face of the central-cylinder, and are not in alternation with the 

 groups of hadrome, here being situated on the ventral face. The 

 groups of hadrome, commonly two, contain a few narrow vessels, but 

 seem, however, in some cases to be. entirely wanting, thus the cylinder 

 looks as if it merely consisted of leptome. The roots showed other- 

 wise a more or less large-celled parenchyma with deposits of starch. 



Two different kinds of organs have been observed as fixing the roots 

 to the substratum: "hairs" with the structure of true roothairs, but 

 with the properties of rhizoids; and the so called "hapters." These 

 last organs have been described more completely in a special paper by 

 the same author 1 . They are exogenous and are constantly developed 

 from the base of the shoots; they show a conical shape as long as they 

 have not yet reached the substratum, but after that they become 

 flattened and show usually a more or less digitate lobation, the lobes 

 closely fastened to the substratum, and exuding a brownish secretion. 

 These "hapters," which remind one very much of similar organs of the 

 Fucacece and Lamhmriacece show a verv simple structure, consisting 

 merely of a parenchymal tissue, in which the author observed the 

 presence of siliceous concretions. The hapters have no root-cap, but 

 are able to regenerate like true roots. 



The shoots are developed in acropetal succession from the sides of 



e flattened roots, or in some cases a little towards the ventral face; 

 they appear usually in pairs, more or less opposite, and are developed 

 from the outermost layer of the bark, without being in contact with 

 the central-cylinder. They resemble the roots fixed to the substratum 

 hy rhizoids and hapters, and are more or less dorsiventral. 



The leaves show a great variation in size and shape; the first de- 

 veloped are scale-like, succeeded by the mostly alternating proper 

 'eaves, the blade of which may vary from simple and very small as in 

 Tristicha and several species of Podosttmon, until larger and deeply 

 c, eft as in most species of this family. 



The paper is illustrated by 17 figures, mostly original and finely 



drawn by the author himself.— Thko. Holm. 



1 Botanische Notizen. Bot. Zeitung, 188. 4 {. 



th 



