709 
Cos tar ia, Undaria , and Laminaria. 
and midrib. As it may not be uninteresting to compare these three 
members of the order, and as some points seem worth mentioning, a brief 
account of the early stages of development is given below. 
Embryonal Stages. 
In my collection the youngest specimen measured 0*45 mm. in total 
length, with a lanceolate monostromatic blade and short stipe. The transi¬ 
tional region was already three-layered, as seen under the microscope by 
varying the focus. Although I was not able to find the confervoid stage of 
the present species, I do not doubt that it may be similar to what has been 
observed in Saccorhiza by Thuret and in Costaria by myself. 
A specimen measuring 1*62 mm. in total length is shown in Fig. 36, 
PI. LV. The greater part of the blade, except a small area at the transitional 
region, is monostromatic. In the apical point we see the coaxial hyperbolic 
arrangement of cells still beautifully regular (Fig. 37). In more advanced 
stages when the blade has attained 4 mm. or more, the complex structure 
in the transitional region is highly developed. The primary hyphal cells 
traverse it longitudinally, having a vein-like appearance, anastomosing with 
the adjacent ones by short lateral branches. The minute structure of these 
cells, together with their relation to the precortical cells, is vividly seen in 
this species, by observing the blade in toto under a microscope. In Costaria 
and Undaria we could not trace the veinlets completely (Fig. 15, PI. LI 11 ). 
Fig. 45, PL LV, is drawn from a specimen with the frond about 2 cm. in 
total length. It is from about the middle part of the blade. In the lower 
portions towards the transitional region, the hyphae gradually become hard 
to trace, as the complexity of the structure makes the preparations less 
translucent. It will be recognized from this figure that room for the passage 
of the hyphae is sought in the intercellular spaces of the precortical cells. 
But this fact is more easily understood when observed in cross-sections 
of the blade at earlier stages. 
Figs. 43 and 44 are cross-sections through the middle part and the 
transitional region respectively of a frond about 5 mm. in total length. In 
the former we see two hyphal cells in section at the meeting points of four 
rectangular precortical cells. An exactly similar figure has been drawn by 
Kiitzing 1 from a four-layered stage of Lamhiaria saccharina , though he 
does not give a full explanation of it. In the transitional region, which 
shows a more advanced state of the tissue, the two layers of the precortical 
cells are separated by the gelatinous matrix interposed between them. The 
hyphal cells are no longer compressed in the intercellular spaces, but have 
a free medium around them. They terminate at the external limit of the 
four-layered area, finally joining on to a comparatively small precortical cell. 
1 Kiitzing: Phyc. Gen., PI. XXIV, I, Fig. 3. 
