Holtz: OBSERVATIONS ON PEI.VETIA. 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 papillae. A well-developed plant may have half a dozen 

 main branches and fifty to sixty laminae. 



When placed in fresh water the mucilage of the interior of 

 the plant absorbing the water, causes the laminae to burst. The 

 distending pith pushes its way out and the cortex curls back, 

 showing a state of tension between interior and exterior. As a 

 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 VII conceptacles are visible on the inside of the cortex 

 in the bursted laminae. 



Minute anatomy ', tissues in general. Pelvctia shows con- 

 siderable differentiation of tissues, though not so much as many 

 other algae, not even so much as some of the other Fucaceae. 

 Fucus shows greater differentiation in having a midrib and air 

 vesicles in addition to the structures possessed by Pelvetia 

 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. 



Epidermis. The epidermal tissue of Pelvetiafastigiata 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 quadrangular or 

 polygonal outline. The epidermis is shown in longitudinal and 

 cross-sections in Figs, i-j, PL IX. 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 



