138* Grubb .— The Attachments of Porphyra umbilicalis . 
6. Discussion of Cases of Epiphytism. 
* 
Although Porphyra is typically a rock-dweller, yet many breakwaters 
stretching out to sea have their vertical sides clothed with the purple fronds. 
Material taken from such a source showed, in longitudinal sections through 
the attachment and substratum, the characteristic structure of a normal disc 
on the exterior of the wood (Text-fig. 7), several fronds with gelatinous 
walls arising from the upper part of the disc, while the external filaments of 
(b) and thickened tissue formed by branching and 
division of the filaments (c). Five fronds with thick 
gelatinous walls (stippled) are being given off from 
the disc. Cells giving rise to the filaments somewhat 
diagrammatic. Camera lucida drawing, x 50. 
Text-fig. 8 . Outline drawing 
of a longitudinal section of Porphyra 
umbilicalis , var. laciniata, on Fucus 
serratus , showing irregular attaching 
base of Porphyra creeping along the 
host. Fig. 5 of Plate I is taken from 
the region a, where the cells of the 
host are disorganized. Cells of host 
and epiphyte somewhat diagram¬ 
matic. Camera lucida outline, x 50. 
the latter had undergone modification and were creeping along the surface 
of the post. The awl-shaped filaments in the interior of the disc had 
penetrated the xylem to a considerable distance, and the cells of the latter 
were very disorganized. Where the threads had met with any considerable 
resistance, they had swollen to an enormous size and formed large circular 
or irregular multinucleate parenchymatous swellings within the tissues of the 
xylem (PI. I, Fig. 3). Where space permitted, the tips of the threads, 
instead of swelling, had cut off cells, each with a single nucleus and 
