220 NEMATOGENZ. 
Orver I], NEMATOGENZ. 
Plants multicellular, or pseudo-multicellular. Cells forming 
a filament (Trichome), usually included in a tubular homogenous 
or lamellate sheath (eagina), Filaments (Zrichomes) either 
simple or branched.—Rabh. Alg. Eur. u., 70. 
Thuret unites Cystiphore and Nematogene in one order under the 
name of Cryptophycee, representing the Cystiphore by a Tribe called 
Chroococcacee and Nematogene by another Tribe termed Nostochinee, so 
that really the difference is only one of name. 
TrisnE 1], NOSTOCHINES. 
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 trichome (hormogonia) which are 
endowed with motion after separating from the mother plant 
=Hormogonee, Thuret. 
The Nostochinee, as interpreted by Messrs. Bornet and Thuret, are 
subdivided into two groups, or sub-tribes. 
Sub-Tribe 1. PsILonEM#& with the filaments not attenuated at one ex- 
tremity to a hair-like thread. 
Sub-Tribe 2. TricHoPHOREs with the apex of the filament attenuated 
to a hair-like extremity. 
Whilst the Chroococcacee reproduce themselves by means of isolated 
cells, the Nostochinez reproduce themselves by the fragments of fila- 
ments (called hoermogones), which are endowed with mobility after 
separating themselves from the mother plant. 
The filaments of Nostochinee are composed essentially of coloured 
cells disposed ina row. This assemblage of cells is]specially 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 isto be 
remembered that the heterocysts are united always with 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 Lyngbya and Scyionema), 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- 
thriz, 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 some perseverance. 
