Costaria, Undaria , and Laminaria. 
707 
Post-embryonal Stages. 
The appearance of the four organs, rhizines, glands, cryptostomata and 
midrib, may be taken as marking the end of the embryonal stages of 
Undaria. The formation of pinnules and sporophylls remains to be accom¬ 
plished before the individual is adult. 
The indications of the pinnules are seen as minute lateral ligules on 
both sides of the base of the blade (Fig. 32). These ligules are shifted 
upwards, increasing more or less in size, as the blade grows at the tran¬ 
sitional region. The result is the dentation of the blade margins near the 
base. New ligules are successively given off below the older ones as the 
plant grows larger and larger (Fig. 33). Full-grown adult plants have 
the blades 1-5-2-0 feet long and 6 -9 inches broad. The ligules follow the 
growth of the blade, extending more in the transverse than in the longi¬ 
tudinal direction of the frond, to form the pinnules characteristic of the 
species. The sinuses between the adjacent pinnules are round, and in some 
forms they are very deep, approaching near the midrib, while in others they 
are comparatively shallow. It is clear from these facts that the extension 
of the ligules takes place in the entire area from the very tip down to the 
midrib. If the meristematic tissue were limited to the area in the tran¬ 
sitional region near the midrib, the ligules should remain as dentations 
along the margin of the blade without adding to their size ; and if it were 
situated in the ligule proper, the sinuses must reach down to the rib. 
At the time when the primary ligules begin to appear, the cylindrical 
stipe becomes gradually compressed. In a middle-aged frond it is ancipitous, 
with prominent margins. The cross-sections of such a stipe show the 
medullary layer in a narrow strip bridging the space between the marginal 
ridges. The greater part of the section consists of thick-walled quad¬ 
rangular cells, disposed in rows radiating from the medullary slit. 
The sporophylls are practically over-extensions of the marginal ridges. 
As a plant approaches maturity, the marginal ridges extend in width as 
well as in length. The rate of growth in length of the sporophyll is far 
quicker than that of the stipe, which is often negligible at this stage. The 
undulation of the sporophyll naturally results. The matured Undaria has 
its stipe almost covered by the ruff-like foldings from both sides. As 
a rule, the extension is gradually propagated upwards from the point of its 
commencement. The point of commencement of the extension varies 
according to the locality where the plant grows. In the northern form, 
which has an enormous length of stipe, it is localized at the basal part of the 
stipe ; in the short-stiped southern form the upper portions of the sporo¬ 
phylls are confluent with the base of the lamina. Moreover, in the southern 
form, sterile ligules from the margins of the sporophylls are generally found, 
