Notes . 
559 
The two remaining species, Z. Dalhousieanum (Spring) and 
Z. Selago (L.), are, to some degree, intermediate types. The phloem 
in Z. Dalhousieanum shows both types, strap-shaped and centric. In 
the branches the structure becomes simpler. There are two narrow 
strips of xylem, with an intermediate strip of phloem, so that a 
prominent row of sieve-tubes occupies the very centre of the stelic 
cylinder. Z. Selago in its structure is modified on that of L . clavatum. 
An interesting feature of Z. Selago and Z. squarrosum is the occurrence 
of root-structures running through the stem. These consist of steles 
containing a crescent-shaped mass of xylem, with protoxylems to- 
wards each tip, while the concave portion is filled up with phloem. 
A characteristic sclerenchymatous sheath surrounds the stele. In 
Z. Selago these root-structures are found even above the point where 
the stem branches, but in Z. squarrosum they have fused with the 
central cylinder before branching occurs. 
C. E. JONES. 
University College, Liverpool. 
REPRODUCTION IN DICTYOTA DICHOTOMA. — i.Diclyola 
is an annual. In this country it germinates during the summer, 
remains small during the winter, grows very rapidly in June, and 
begins to form its reproductive cells in July. 
2. The tetraspores are produced throughout the season, and all 
stages may be found together on the same plant. The sexual cells, 
however, show a remarkable periodicity. The formation, maturation, 
and liberation of each crop occupies a fortnight, the interval between 
two spring-tides. The sori are formed during neap-tides, and the cells 
are liberated during or immediately after the highest spring-tides. 
3. When liberated the oospheres are not invested with walls. In 
this condition they strongly attract the antherozoids, become fertilized, 
and at once start germinating. The plantlets are similar to those 
figured by Thuret as resulting from the germination of the tetraspores. 
4. If not fertilized the eggs lose the power of attracting anthero- 
zoids, they form walls, and, as already described by Thuret and 
Bornet, they germinate parthenogenetically. After one or a few 
divisions, sometimes accompanied by formation of a rhizoid-rudiment, 
the process stops and the plantlets die. 
5. Towards the close of the season some sori fail to mature within 
