Costaria , Undaria , and Laminaria . 713 
3 , 5 ~ 4*5 mm. m diameter, are provided with well-developed lacunae. But 
in a specimen collected late in June the lacunae are generally narrow and 
slit-like, although their number may be quite as great as in the August 
specimens. Unfortunately, I have no set of specimens from April to June, 
and so am unable to trace the exact stage of the plant when the lacunae 
begin to appear. It is a fact, however, that the lacunae in our species are 
not formed until the frond has attained a considerable height. The period 
when the first-year plant has ceased its quick growth in length and begun 
to add to its width may probably be the time of lacunae-formation. 
General Concxusions. 
1. The earliest stage of development of the sporelings of the Laminaria- 
ceae investigated is a confervoid body growing by a single apical cell. The 
confervoid body becomes monostromatic in the next stage, with a mono- 
siphonous stipe. The growth of the monostromatic blade is initiated by 
the two cells situated side by side at the same level beneath the apical cell, 
the axis of the blade passing between the two cells. 
2. The monostromatic blade becomes distromatic at its base; the 
monosiphonous stipe becomes polysiphonous at the same time. A new 
meristematic tissue begins to appear at the transitional region between the 
blade and the stipe. 
3. The growth in length as well as in breadth is due, at a certain period, 
to both the apical and the stipo-frondal growth. The apical growth is 
gradually retarded, and finally ceases. Erosion of the apex of the blade 
follows next. 
4. A single precortical layer of large parenchymatous cells is generated 
at the transitional region between the already-existing two layers. The 
former soon becomes two-layered, and adds to the number of its layers 
later on. Additions of layers of cells are, as a rule, limited to, and begin at, 
the transitional region. 
5. The hyphal cells are generated as the precortical layer becomes 
doubled, and the expansion of their distal ends into a trumpet shape takes 
place at the intercellular spaces. 
6. The rib and the meridional region are formed by special thickening 
of the cortical layers. The dorsiventrality of the lamina, if it exists, is 
indicated simultaneously with the formation of such parts. 
7. In Undaria the mucilage glands are developed at an early stage, 
but in Laminaria the appearance of the lacunae does not take place before 
the blade has attained to a considerable length. 
8. The cryptostomata in the Laminariaceae are not generated from 
a single initial cell. Each hair has its origin in an epidermal cell of equal 
value, except that those in the middle develop earlier than the peripheral cells. 
