Grubb .— The Attachments of Porphyra umbilicalis . 133 
Porphyra is very rarely found epiphytic, but two specimens of P. var. 
laciniata growing on F?ic 7 ts serratus were obtained from Shanklin, and these 
were fixed, embedded, and stained as above. Also some embedded material 
of var. laciniata growing on a post of an old breakwater at Pegwell Bay, 
Kent, was kindly given me by Dr. Delf, to whom my most grateful thanks 
are due both for this and some slides which she had previously made from 
it, and also for her helpful criticism and suggestions throughout. Microtome 
sections of this material were stained in safranin (thirty minutes) and very 
dilute methylene blue (three minutes), and it was found that this double 
stain differentiated clearly the woody tissue and the hypha-like threads of 
the attaching disc. 
4. Description of the Disc. 
The attaching organs of the British species of Porphyra have not 
previously been described in detail, though they are mentioned by several 
writers on the Bangiales. Harvey (6) states that the minute disc is always 
present, and in the species with an upright thallus is accompanied by 
a short linear stipe which is absent in the horizontal thallus of P. laciniata , 
Ag. The internal structure of this disc has been examined by Thuret 
( 9 , p. 59), who notes that in var. vulgaris the discs are formed by ‘ des 
prolongements radiculaires 5 of the lower cells of the thallus, and this is 
corroborated by Berthold ( 1 , p. 3), and Hus ( 7 ), who adds that these thread¬ 
like projections may swell up in contact with the substratum. The only 
other fact recorded in regard to these attachments is that Thuret ( 9 ) believes 
that the reproductive cells may be formed from the actual cells taking part 
in disc formation, but this is denied by later writers. 
On examination these minute attaching organs were found to consist 
typically of discs, circular in outline and from 0-5 to several mm. in 
diameter, which adhere firmly to the substratum of wood or stone. In 
longitudinal section it is seen that this tenacious structure is made up of 
interwoven filaments formed as outgrowths from either surface of the thallus 
cells. The vegetative thallus is originally one cell thick, and in the upper 
part of the disc the single layer of cells is continued down the centre of the 
structure. (Cf. Text-fig. 1, C.) 
The thallus cells are typically brick-shaped and possess a stellate 
chromatophore with radiating arms, the ends of which are flattened against 
the cell-wall, a central pyrenoid and a lateral nucleus lying between the two 
arms of the chromatophore. On dissection the young filament is seen to 
arise as a short blunt protuberance (Text-fig. 2, a); when this is about equal 
in length to the cell itself, a portion of the arm of the chromatophore 
nearest to the growing tube breaks off and passes down to the tip of the 
young filament; at the same time the nucleus divides and the daughter 
nucleus passes into the filament (Text-fig. 2, a) ; as the latter elongates, 
