Some Aspects of the Alga. 45 
responsible. The Leaf-form is recognised, here as elesewhere in 
the plant-kingdom, as a primary adaptation to light, and its modifi¬ 
cations are discussed. 
It is, of course, sufficiently obvious that the fact of these 
various vegetation-forms being well fitted to live under the various 
conditions in which they occur is no explanation of the origin of 
the forms in question, since algae of various forms live side by side, 
and we are often quite at a loss to understand the origin of their 
differences inter se. 
The various types of Epiphytes, Endophytes and Parasites are 
fully described and illustrated, and the transitions between them 
indicated. 
A very useful section is devoted to Plankton. The literature of 
this subject has increased enormously in the past decade; it is very 
widely scattered and much of it is rather inaccessible. Professor 
Oltmanns brings together the main facts and principles in his short 
but judicious account. 
The adaptations of algze which live partly or wholly out of 
water also forms the subject of a short section, and the different 
forms are distinguished. While some, mostly unicellular forms 
(PIeurococcus, etc.), simply lie or are fixed in situations where they 
are liable to drying, a few others— Protosiphon, Botrydium, (Edo - 
cladium, species of Vaucheria and Stigeoclonium , are strictly terres¬ 
trial, and have an absorbing root system like the higher plants. 
The former not only resist drying up with great success, but in some 
cases it has been shewn that long drying is necessary to their 
resting cells to enable them to germinate. 
In the section on Symbiosis, a short account of Lichens is 
given, and then the association of unicellular algae with various 
animals is described. In regard to the green cells of Convoluta 
Rosco/pensis attention should be called to the work of Keeble and 
Gamble, 1 who have made a very full study of this particular case of 
symbiosis, correcting many of the older statements. These authors 
have quite recently 2 shewn that the alga is a quadri-flagellate 
Chlamydomonas which enters the young animals from the egg 
capsules, on which a rich flora lives. It is interesting to notice that 
in one of Haberlandt’s figures reproduced by Professor Oltmanns, 
the whole structure of the “green cell” shewn corresponds exactly 
with the Chlamydomonas-t ype. 
Finally an account is given of the symbiosis of various algte 
with Sponges. 
1 Quart. Journ. Micr. Sci., 1903. 
a Proc. Roy. Soc., B. 77, 1905, 
