Delf . — The Attaching Discs of the Ulvaceae. 405 
Fig. 1). Thuret states that the tubular filaments may reach a length of 
6-10 mm., but those measured by me were never more than 3 mm. in length. 
The superficial cells of the thallus giving rise to the filaments seem to 
be always multinucleate. In their upper region from three to five nuclei 
have usually been observed (PI. XLV, Fig. 8). The tubes are exceedingly 
narrow, and are smaller when running on the outside than when running in 
Text-fig. 2. Diagram of longitudinal section through disc of Ulva latissima. The oblique 
lines show the general direction in which the filaments run. The dotted regions show the false 
tissue formed by the large and small filaments at the periphery of the disc : the region around A is 
that from which PI. XLV, Fig. 7 is drawn in detail. At B is the lower part of a frond formed from 
an outgrowth of the disc. 
the interior of the thallus (PL XLV, Fig. 8, at a) ; in either case minute nuclei 
occur at intervals down these tubes, and from two to five nuclei are 
commonly found crowded together in the tips of the tubes. These apices 
vary very much in size ; they are usually narrow and pointed, with small 
nuclei, until the periphery of some part of the disc is approached, when 
they increase greatly in size, the nuclei become larger and more numerous, 
