i37 
Grubb .— The Attachments of Porphyra umbilicalis. 
the British species of Porphyra , but whether the discs perennate during the 
summer season when the fronds are absent, and put up new fronds in the 
autumn, has not yet been ascertained. 
5. Sporelings. 
It was noted at Swanage that the young fronds of Porphyra were 
usually found growing either in connexion with circular dark patches of the 
blue-green alga, Rivularia atra , or else among a layer of debris on the 
rocks, composed of mud and filaments of microscopic algae. This is 
probably not a case of symbiosis, as it does not always occur, but it is 
Text-fig. 5. Outline drawing of a young 
sporeling ot Enteromorpha covipressa , showing the 
creeping prothallial base (one layer of cells thick) 
and tAvo linear fronds arising from it. Drawn with 
camera lucida. x 60. 
Text-FIG. 6 . Outline drawing 
of the base of the sporeling seen in 
Plate I, Fig. 2, showing the first six 
rhizoids enclosed partially in a gela¬ 
tinous sheath. Camera lucida draw¬ 
ing. x 650. 
likely that germination takes place more readily in this substratum as the 
debris serves to protect the sporlings in rough weather. Even when no 
fronds were visible to the naked eye, dissection and examination of the 
tangled material would occasionally reveal a sporeling. The youngest plant 
thus dissected out was only 0-34 mm. in length and 0-03 mm. at its widest 
point; it consisted of about seventy to eighty cells, a large proportion of 
which were modified to form rhizoids (PI. I, Fig. 2). Four of these had 
elongated greatly, and of these one had a swollen tip and. another was 
branched to form a clasping organ at the base (Text-fig. 6). The formation 
of filaments which will later combine to build up a disc takes place there¬ 
fore at a very early stage. 
