6 gS 
Yendo.—The Development of 
monostromatic part first formed seems to have never decreased in its area, 
nor does the distromatic, &c. In other words, the areas of simpler structure 
do not add any complexity to the tissue by the later development except 
for the extension in area. The additions of new elements always commence 
in the transitional region. 
Close examination under a higher power of the microscope shows, how¬ 
ever, that the boundaries are not in straight lines, but very irregularly 
serrated. Setchell 1 mentions a similar condition in the youngest fronds of 
Saccorhiza dermatodea. Besides, there are many small areas detached from 
the principal part, but with a similar addition of layers. This is especially 
the case for the distromatic layer. Such oases must have resulted from an ab¬ 
normal meristematic activity retained in the cells of the monostromatic area. 
Fig. 16, PI. LIII, illustrates a part of the lamina under such a condition, the 
shaded part signifying a di- or tri-stromatic area ; Fig. 17 shows one of the 
oases still more magnified. The irregularity of the border line is due 
to the fact that certain cells in a group—areoles of cells as it were—which 
have been derived shortly before from the same mother-cell are simul¬ 
taneously divided into two layers. Fig. 19 shows a part of Fig. 16 under 
a high power. 
Klitzing 2 seems to have observed a similar structure in an embryonal 
blade of Laminaria saccharina . He remarks: ‘Man bemerkt, dass an 
einigen Stellen die Randzellen sich in kleine Kiigelchen aufgelost haben, die 
je 4 und 4 zusammenstehen (Exanthem ?).’ He seems to have regarded the 
areolar cells as having a pathological origin. I am rather inclined to sup¬ 
pose, if I may be allowed the suggestion, that his specimens had the 
epidermal cells plasmolysed. 
In Costaria Turneri the apical portion of the blade remains in its 
monostromatic state for a considerable time. I found several specimens 
measuring 3-4 cm. in length, with the three costae already formed, which 
still had the apical region in a single layer of cells. 
Similar stages of development—polystromatic lamina with mono¬ 
stromatic apex—have been recorded by Klitzing, Kuckuck, Reinke, 
Setchell, Griggs, &c., in Laminaria saccharina , L. ephemera , Saccorhiza 
dermatodea , Alaria esculenta , &c. The present writer has collected many 
specimens of Unaaria and Laminaria with a similar structure. Hence, 
it may be safely stated that most members of the Laminariaceae have once 
passed through such a stage during their life-history. 
In Costaria Turneri , some species of Laminaria , and certain others, the 
apical growth seems to continue, however, in a slighter degree than before, 
even after the greater part of the blade has become polystromatic. It 
1 Setchell: Concerning the Life-history of Saccorhiza dermatodea. Proc. of Amer. Acad, of Art 
and Sc., 1891, p. 182, Figs. 1 and 2. 
2 Klitzing : 1 . c., p. 345. 
