324 Mr. J. Ralfs on the Nostochinee. 
often rendered useless by the separation of the filament into 
single cells. The destruction of the filament is attended by the 
escape of the colouring’ matter, which stains the water or what- 
ever 1s in contact with the mass, and is usually the first sign of 
that destruction. 
i find the best method of preserving specimens is to dry them 
as quickly as possible on tale or glass. Specimens preserved on 
paper can rarely be removed without injury. In examining spe- 
cimens that have been dried, it is necessary to bear in mind, that 
although, when revived by adding a little water, they present cha- 
racters apparently but little altered from their recent ones, yet 
their joints are then more distinct and orbicular from contraction 
at their junction ; hence a cell quadrate in the reeent plant will 
be orbicular in the revived one. I have elsewhere mentioned 
that from a similar cause the dried frond in Closteriwm appears 
more attenuated at the extremities than is natural, and I fear 
that from inattention to this fact descriptions taken from dried 
specimens are sometimes faulty. 
Until the publication of Professor Kiitzing’s ‘ Phyeologia Ge- 
neralis,’ the described species belonging to this group were few 
in number, and usually retamed im a single genus either as Ana- 
baina, Bory, or Spherozyga, Ag. Professor Kiitzing has now 
determined upwards of thirty species, which he has distributed 
in four genera*. 
Attempts to ascertain the earlier synonyms in tribes which 
require the aid of the microscope to detect the generic and spe- 
cific differences are necessarily attended with much difficulty. 
Not only are our present instruments far superior to those used 
a few years ago, but when natural history began to take its 
proper rank in science, the higher tribes sufficiently taxed the 
time and skill of collectors and writers; it is therefore not sur- 
prising that the more minute Cryptogamia should have been 
comparatively neglected. The descriptions were chiefly taken 
from characters obvious to the naked eye, and besides were often 
so brief and at the same time so vague, that they were equally 
applicable to members of very different genera ; hence authors, 
unable to determine with certainty the species of their prede- 
cessors, were frequently compelled either to depend on chance in 
* TI take this opportunity of directing attention to his ‘‘Tabule Phycolo- 
ice,’ now publishing in numbers in a cheap form, and containing magnified 
figures of every species known to him. To those who wish to identify our 
British freshwater Algze it is indispensable. Of British species of Oscilla- 
toria we have no figures of the slightest value, for unfortunately Mr. Hassall, 
many of whose figures in other genera are very useful, has, in every figure 
which he has given of that genus, omitted to give the ends of the filaments, 
though they are often essential to the determination of the species. 
