On THE PlTHOPHORACEyE. 



11 



knowledge of the nature of this difference. I think it not improbable, 

 that an extremely thin layer upon the surface of the cell-membrane has 

 been transformed from cellulose to a jelly. — As a rule the helicoids 

 occur only on terminal cells, but now and then such organs are formed 

 also on inclosed cells (pi. 5, fig. 1). — Regarding the function of the 

 helicoid cells, the name at once indicates that it is principally to be 

 an attaching organ of the plant. They are particularly well adapted to 

 this purpose by the form which their upper part, the helicoid, has 

 assumed. That they also have another purpose to serve, is very clearly 

 hinted by the nature of their contents. The chlorophyll-coloured proto- 

 plasm, which exists in such uncommon abundance, especially in the 

 helicoid itself, no doubt officiates in the usual manner, and therefore the 

 helicoid cells may reasonably also be regarded as active organs of 

 assimilation. ] ) That they have besides, like other cells of the plant, the 

 power of absorbing liquid food for the plant, must be clear in itself. 



II. ON THE REPRODUCTIVE ORGANS AND THEIR FORMATION. 



The reproduction of Pithopkoracece is effected in two ways, viz. l:o 

 by the formation of spores, and 2:o by the bringing forth of prolific 

 cells. — Let us first describe the formation of spores. As I have had 

 opportunity to observe it step for step only in P. kewensis nob., what I 

 am going to say has its full bearing onhy on this species, but all signs 

 seem to indicate, that the formation of spores in the other Pithophoracece 

 is effected, in all essential particulars, in the same manner. Formation 

 of spores takes place, as a rule, only in the cauloid part of the thallus; 

 but each cell in this part has the power of bringing forth a spore. 

 Thus, spores may be formed by the terminal cells as well as by the 

 inclosed, by the cells of the principal filament as well as by those of 

 the branches. It is, however, rather rare to find specimens, in which 

 all the cells of the cauloid have really brought forth spores (such a 

 specimen of P. Cleveana nob. is represented plate 2, fig. 12); generally 

 the formation of spores has failed in one or more cells. Cells which 

 have neither formed nor will ever form spores are not rare in the prin- 

 cipal filament of the cauloid; in the branches, on the contrary, sterile 



J ) Thus the hclico'ids of Vdliophoracccc show a double analogy to the tendrils 

 of certain phanerogamous plants, for instance with those of the l J KSS/Jfortce. Both 

 are parts of the stem, transformed into attaching organs, and both are besides at the 

 same time active in some degree in the assimilation. 



