220 NEMATOGEN.E. 



ORDER II. NEMATOGENJE. 



Plants multicellular, or pseudo-multicellular. Cells forming 

 a filament (Trichome), usually included in a tubular homogenous 

 or lamellate sheath (vagina). Filaments (Tricliomes*) either 

 simple or branched. Ralli. Alg. Eur. n., 70. 



Thuret unites Cystiphorce and Nematogence in one order under the 

 name of Cryptopliycece, representing the CystiplwreB by a Tribe called 

 Chroococcacecs and NematogencB by another Tribe termed Nostochinece, so 

 that really the difference is only one of name. 



TRIBE 1. NOSTO CHINESE . 



Trichomes simple or branched, with an obtuse, or acute and 

 setiform apex, either naked or enclosed in a sheath. Repro- 

 duction by fragments of the trie-home (liormogonia) which are 

 endowed with motion after separating from the mother plant 

 =Hormogonece. Thuret. 



The Nostochinees, as interpreted by Messrs. Bornet and Thuret, are 

 subdivided into two groups, or sub -tribes. 



Sub-Tribe 1. PSILONEM.E -with the filaments not attenuated at one ex- 

 tremity to a hair-like thread. 



Sub-Tribe 2. TRICHOPHORE^E with the apex of the filament attenuated 

 to a hair-like extremity. 



"Whilst the Chroococcacea? reproduce themselves by means of isolated 

 cells, the Nostochineae reproduce themselves by the fragments of fila- 

 ments (called liormogones), which are endowed with mobility after 

 separating themselves from the mother plant. 



The filaments of Nostochinece are composed essentially of coloured 

 cells disposed in a row. This assemblage of cells isjspecially designated 

 a trichome. The trichome is either naked, or immersed in mucilage, or 

 enclosed in a sheath. 



The presence or absence of heterocysts, their number, their situation 

 in the filament, are characters important to note, but which hitherto 

 have been much neglected. Easily recognized in the living plant by 

 their yellow colour from the other cells of the trichome, but sometimes 

 difficult to distinguish in dried specimens. In doubtful cases it is to be 

 remembered that the heterocjsts are united always Avith the sheath, and 

 if that envelope is defective in the other cells it will suffice to apply an 

 appropriate re-agent, such as potass, solution of iodine, &c., to obtain 

 evidence of their nature. 



Sometimes the terminal cells of the trichome resemble the others (as 

 in Lynghya and Scytonema), sometimes the filaments are terminated by a 

 hyaline hair, elongated and deprived of its coloured contents, with a 

 diameter much less than the ordinary joints of the trichome (as Calo- 

 thrix, Rivularia, &c.). This distinction, which corresponds in another 

 instance to the principal growing point of extension of the filaments, is 

 very marked in the living state, and especially in individuals in full 

 vegetation. When, on the contrary, the plants are old, and the summit 

 broken and their hormogones dispersed, the complete filaments are 

 sometimes very rare, and must be sought with sonic perseverance. 



