The Attachments of Porphyra umbilicalis, (L.) J. Ag. 
BY 
VIOLET M. GRUBB, B.Sc. 
With Plate I and eight Figures in the Text. 
i. Introduction. 
B ASAL holdfasts are organs which are characteristic of the vast majority 
of marine algae, and are found exhibiting every degree of complexity 
from simple rhizoids to massive hapterons. 
The attachment in the Rhodophyceae consists generally of a disc or 
root-like structure composed originally of filaments formed by the out¬ 
growth of the lower cells of the thallus ( 5 ). These filaments may lose 
their individual structure and become welded into a solid parenchy¬ 
matous mass ( 5 ), but whether this takes place or not the adherence of 
the basal organ to the substratum is surprisingly strong and adequate to 
withstand the constant strain to which marine algae are subjected, for 
a longer or shorter period each day, by the movement of the waves. 
Certain genera are invariably found as epiphytes or parasites, but the details 
of their attachments have only been worked out in a few cases. In the 
well-known case of specialized parasitism—that of Polysiphonia fastigiata 
on Ascophyllum nodosum —the attaching filaments are recorded as penetrat¬ 
ing among the cells of the host but not actually entering them ( 8 ). 
2. Habit and Growth of the Species of Porphyra. 
During certain seasons of the year Porphyra is one of the most common 
of the red algae that inhabit the coasts of the Northern Hemisphere, and 
considering its frequency it is curious that its interesting method of attach¬ 
ment has never been investigated in detail. The material for this account 
was obtained mainly from Durlston Bay, near Swanage, where thd three 
varieties of Porphyra umbilicalis , (L.) J. Ag., occur—var. linearis , Grev., var. 
vulgaris , Ag., and var. laciniata , Ag. 
During the summer months there is no sign of the purple fronds, but 
about November the rocks become covered with sheets of the narrow 
ribbons ; this narrow form was originally separated as a different species 
[ Annals of Botany, Vol. XXXVII. No. CXLV. January, 1923.] 
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