318 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
is far from precise. Cellulose with a little pectin in the Peridinieae ; 
pectin without cellulose in the Diatomaceae ; cellulose as a general rule 
in the Chlorophyceae (with the exception of the Siphoneae, where 
cellulose is disputed and callose and pectin affirmed) ; both cellulose 
and pectin in the Phaeophyceae and in the Florideae. A. G. 
Critical Study of certain Unicellular Cyanophyceae from the 
Point of View of their Evolution.— W. B. Crow (New Phytologist, 
1922, 21, 81-102, fig.). An analysis of the characters of certain 
unicellular Chroococcaceae with a view to ascertaining their importance 
in the evolution of the group, and hence in helping to establish a satis- 
factory system of classification. The work proceeds under the following 
headings : Cell-form, cell-size, internal structure of cell, mucilage, 
pigment, planes of cell-division. Some of these characters, such 
as orientation of planes of division, cell-form, cell-size, have long been 
in use as systematic distinctions. The presence of pigments, pseudo- 
vacuoles, and stratified membranes may also be of importance. Further, 
the differentiation of the protoplasm, and particularly the distribution 
of the pigment, are very significant, though not yet appreciated in 
schemes of classification. On the other hand, the character of the 
stratum or colony is of but slight morphological significance, and 
should not be too much trusted by systematists. The author holds 
that the most prominent indications of the primitive character of the 
Hhroococcaceae are the production of several pigments in the plasma ; 
the variability of these pigments in amount and distribution ; the 
unspecialized character of the envelope, and its pectic nature ; the 
variability in the differentiation of the layers of the protoplasm, including 
the plasma-membrane, so that sometimes the cell may be homogeneous ; 
also the lack of a definite chloroplast and a nucleus. The complete 
absence of flagella in the Cyanophyceae is a remarkable featuie, which 
may or may not be a secondary character. A. G. 
Determination of the Optimum of Humidity required by the 
Oscillarieae. — Henri Coupin ( Gomptes Rendus, Paris, 1922, 174, 
822-4). These algae, when cultivated in a vessel of water, congregate 
at the edges and raise themselves to nearly 1 cm. on the sides. They 
do the same in nature. The author seeks to know the reason for this, 
whether it is due to needs of oxygenation, of light, of osmosis, of degree 
of humidity, etc. To test the question of humidity he prepared jellies 
of various strengths of gelose in fresh water and in Knop’s medium, 
and sowed Oscillaria on the surface. The alga succeeded best on jellies 
containing 1 p.c. of gelose, but less well or not at all on stronger and 
on more watery jellies. There is thus an optimum of humidity ; and 
it may be that in nature, when climbing the walls or margins of pools, 
they are seeking the limit of relative dryness that is compatible with 
their existence. Water they need, but in moderation. A. G. 
Heleoplankton of Three Berkshire Pools. — B. Millard Griffiths 
(, Journ . Linn. Soc. Bot., 1922, 46, 1-11, 1 pi.). The three pools are 
near Beading, and have been artificially dammed up in stream valleys. 
A total of 65 algae was obtained from them, and their distribution is 
