Holtz: OBSERVATIONS ON PELVETIA. 25 
of the lobe. Occasionally conceptacles are scattered over the 
stipe. These are generally less mature than those on the 
lamina above. They may be formed here adventitiously after 
those of the lamina, or else they may have been formed before 
or at the same time as those on the lamina and were then ar- 
rested in their growth. 
The conceptacles cause a small papilla in the surface above 
them. This can be easily seen with the naked eye, as can also - 
the ostioles themselves, which appear as little pits in the tops of 
the papilla. A well-developed plant may have half a dozen 
main branches and fifty to sixty lamine. 
When placed in fresh water the mucilage of the interior of 
the plant absorbing the water, causes the lamine to burst. The 
distending pith pushes its way out and the cortex curls back, 
showing a state of tension between interior and exterior. Asa 
result the cortex pulls off from the pith. The conceptacles then 
appear plainly as little spherical masses projecting from the 
inner side of the cortex. This intimate union of the conceptacle. 
with the cortex might be taken as evidence of the cortical 
origin of the conceptacles, which is the case, as will be shown. 
In Plate V/T conceptacles are visible on the inside of the cortex 
in the bursted lamine. 
Minute anatomy, tissues in general. — Pelvetia shows con- 
siderable differentiation of tissues, though not so much as many 
other algz, not even so much as some of the other Fucacee. 
Fucus shows greater differentiation in having a midrib and air 
vesicles in addition to the structures possessed by Pelvetza 
fastigiata. 
There are three principal tissues in the body of the plant. 
The epidermis, cortex and pith comprise the main bulk of the 
body. In the holdfast, however, no real pith cells are found. 
Eipidermis.—TVhe epidermal tissue of Pelvetza fastigvata con- 
sists of a layer of prismatic cells elongated radially to about 
twice their shorter diameters, which are about equal. The epi- 
dermis is best developed in the stipe and lamina. Seen here 
in surface view the cells present a roughly quadranguiar or 
polygonal outline. The epidermis is shown in longitudinal and 
cross-sections in /7gs. 7-3, Pl. 7X. The inner end of the 
epidermal cells and their radial walls are thin, while their free 
surface walls are convex outward. The surface of the epi- 
dermis is covered with a cuticle, thick and striated. This 
