191 
It is interesting in this connection alone to compare the winter 
with the summer flora. Species of the hardy genera of Algae 
(Cladophora, Rhizoclonium, Oedogonium, Ulothrix) are gps 
to be found just only in winter a 
such considerable quantity ; but the more delicate species on ly 
put in an app en the temperature and, wha obably 
more important, the amount of light* has increased. Much can be 
said on this subject, but I must here confine myself to the state- 
ments made 
The plankton of the artificial waters at Kew is, as has already 
been mentioned, in its general character almost the same as that o 
the Thames, and for this reason I have included species found in 
ihe plankton of the river at Kew in my list. In quantity of 
individuals, however, the difference is very striking ; whereas the 
8 pia 
the waters at Kew the green j rre (especi wn f Vilocinet Pedia- 
strum, and Scenedesmus) play a very important part and consider- 
wu exceed the Diatomaceae in number. This striking difference 
n the quantitative development of the plankton in rivers and 
mien has already been pointed out by Zacharias and others. On 
the whole, d the plankton of the artificial waters at Kew 
is rather poo 
If the ce of the flora, as tabulated on page 188, be once 
more referred to, it will be noticed that the number of species of 
Desmids fou is i 
represented. Of the large genus Stawrastrum only six species, 
uastrum only one species was found, whilst Micrasterias, 
Desmidium, &c., are quite a t 
The entire absence of Peridineae is worthy of note. 
* * > * Ld 
The Algae in the subjoined list were for the most part collected 
by me from the beginning of December, 1901, to October, 1902. 
Ag the collecting was carried out in different parts of the gardens 
almost daily, not many of the forms present this year will have 
escaped me. A preliminary list of Algae, collect d by Mr. C. H. 
Wright, A.L.S., and Mr. G. Massee, F.L.S., s placed in my 
hands at the commencement of this hreig; many of these 
have been found again this year, but some twenty I quote on 
their authority. These species have been marked with an asterisk. 
Journal of the Royal Microscopical Society, 1897, p. 511, mentions 
a number of Algae he had found at Kew, which have also been 
adopted in the present list. 
A few words on the system of classification adopted may be 
added. For many years the old system of classifying Algae has 
been felt to be inadequate, and in recent years an attempt has 
* Cp. Zacharias, Uber die Ursache der der Verschiedenheit des Winterplanktons in 
grossen u. kleinen Seen. Zoologischer Anzeiger, Bd. xxii., 1889, pp, 26 and 27, 
