139 
Grubb. — TJie Attachments of Porphyra umbilicalis . 
vacuolated protoplasm, and these cells are seen as circular patches with 
gelatinous walls within the woody tissues (PL I, Fig. 4). The penetration 
of the host appears to be very complete, for the wood of the post is dis¬ 
organized and riddled with these parenchymatous masses and tissues 
of cells. 
In the case of the material of Porphyra umbilicalis on Fucus serratus , 
the thallus of Fucus was attached when found near low-water mark, but the 
serrated lamina had completely disappeared and only the midrib of the 
frond was left ; at the top of this a plant of P. laciniata was found growing. 
Sections showed that it was attached, by a large spreading base formed 
in the usual way from interwoven filaments, and giving rise at the edges to 
new fronds (Text-fig. 8). As the winding filaments approached the host, 
they branched frequently and the ends became swollen and gelatinous, but 
cross-walls were not found so commonly as in the material on the post. 
The threads had a forcible boring action and penetrated both between and 
into the cells of the thallus, and could be seen to a great depth traversing 
the cells of the cortex and branching within the cell cavities (PI. I. Fig. 5). 
The cells of the host were full of contents and appear to have been living, 
but penetration of the filaments of the disc rapidly induced disorganization. 
The filaments of the attaching disc of Porphyra , therefore, show 
a capacity for penetrating into as well as between cells of a cellular host, 
though the alga is typically a rock-dweller. From the fact that the 
filaments bring about death and disorganization of the cells of the host, it 
must be inferred that there is no symbiotic relationship present in this case ; 
on the contrary, in this, the first recorded examination of a British species 
of Porphyra growing on a living host, practically all conditions of true 
parasitism are fulfilled. 
7. Summary. 
1. The three varieties of Porphyra umbilicalis , var. linearis , var. 
vulgaris , and var. laciniata , grow commonly in exposed positions and are 
attached to the rocks, &c., by minute adhesive discs. 
2. Observations corroborate the view put forward by Flarvey that the 
narrow form of frond known as var. linearis is only a growth-form of var. 
vulgaris. 
3. The attaching discs of Porphyra are capable of lateral extension 
and may proliferate into new branches. 
4. The disc is made up of numerous interwoven threads of two kinds 
which are formed as outgrowths from the thallus cells: 
(1) long slender filaments ; (2) short stout ones from the lowest cells. 
5. Filaments near to, or in contact with, the substratum swell up and 
branch or produce suckers or hapterons. Filaments on the exterior of the 
disk may produce a parenchymatous tissue by branching or division. 
