204 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



the perforations, is more numerous in the subHtoral zone 

 than in the litoral zone/ or perhaps the light has something 

 to do with it; but whatever the cause, both the anatomical 

 and morphological differences are too slight to allow us to 

 consider the sublitoral zone form a variety of the typical 

 Poi'fhyra -perforata J. Agardh. 



The shape of the frond of Porphyra -perforata is as a 

 rule linear-lanceolate, with an undulate margin and a cor- 

 date base. But frequently more or less expanded, broadly 

 laciniate fronds are met with, which possess an umbilicate 

 base. Between these two extreme forms which the frond 

 may assume, numerous transition stages are found. 



The size of the frond is variable. Fruit has been found 

 on specimens but seven centimeters long. A well-devel- 

 oped specimen usually measures from 50-70 centimeters. 

 Both size and shape of the frond depend apparently largely 

 upon local conditions. For instance, those plants which 

 grow on the rocks in the upper part of the litoral zone 

 seem but seldom to attain a great development, and are 

 usually lanceolate. Those which grow in the elitoral zone 

 or in places where they are exposed to the tow of the tide 

 and are always, or for the greater part of the time, stretched 

 out by the water — such as those which grow on lagoons 

 and on long, low reefs, — are more linear-lanceolate, while, 

 as has been said before, those growing on rocks exposed 

 to the irregular wash of the waves are much laciniate and 

 rather broadly expanded. 



The plants are attached by a disc, the structure of which 

 is of much interest. It agrees in all respects with that of 

 P. laciniata as described by Bornet (1878). P. perforata 



1 Von Martens (1866), in a discussion on the use of seaweed as food by marine ani- 

 mals, describes some specimens of P. vulgaris Ag. (?) which were covered by a large 

 number of sea-slugs {Nasa cornkulum Olivi), and which were much perforate. In their 

 immediate vicinity grew plants of Grateloupia filicina and of C hietonwrpha lintitn, which 

 w^ere not inhabited by the slug and had not been damaged. From this he concludes 

 that the perforate condition of the specimens of P. vulgaris was due to the action of 

 the slug, which used the plants for nourishment. The slug which infests the plants 

 Porphyra perforata on the Califoruian shores is a species of Lacuna. On this subject 

 Agardh (18S2) says: " * * * ; prseterea frequenter foraminibus rainutis rotundatis, 

 linsem aut paucas diametro cequantibus, prsecipai in disco perforatam vidi, et hoc 

 quidem aliquando jam in speciminibus minoribus et angustis." 



