TRANSACTIONS OF SECTION D. 711 



contain one nucleus : in other cells usually several nuclei appear : iu the larger 

 ones as many as thirty or forty may frequently be counted. In some of the inner 

 cells of the cortex each nucleus is surrounded by a crowd of chromatophores. 



There appears to be an absence of hyphal tissue in the stalk below the ridge. 

 The cells of the hapteres are parenchymatous ; they are of two kinds, larger and 

 smaller cells alternating in such a manner that the larger cells appear to be surrounded 

 and separated by the smaller. There is in the hapteres no strand of conducting 

 tissue ; in this respect the hapteres resemble those of Podostemaceae. Numerous 

 multicellular root-hairs are developed from the part of the haptere in contact with 

 the substratum. This is due to the outg^rowth of epidermal cells. The formation 

 of sporangia takes place in exactly the same way ; and these bodies occur on the 

 inside as well as the outside of the hollow bulb. 



The difference between L. bidbosu and allied species is seen as well in the 

 formation of the bulb and stalk as in the position of the sporangia. The shedding 

 of the lamina does not appear to be recorded for L. bullosa. 



The differentiation of the stalk is primarily due to the necessity of supporting 

 the huge lamina. The cylindrical stalk of young specimens points to the descent 

 of the species from a form more nearly allied to that of other Laminarias, where 

 the stalk is still rounded. It is not easy to assign a definite reason for the 

 departure of the stalk from its cylindrical form. 



There are in this species a great amoimt of morphological differentiation and 

 complicated attempts at adaptation. There does not appear to be the same amount 

 of histological differentiation. It has not been possible to examine old specimens; 

 but, so far as material extends, no zones of secondary thickening have been met with, 

 neither have any mucilage-ducts been observed : the development of sieve-hyphse 

 is not at all well marked. Finally, the huge size of the cells and their numerous 

 nuclei, and the increase in size by the growth of cells rather than their division, seem 

 to point to a low stage of histological differentiation. 



5. On Pachytheca, a Silurian Alga of doubtful Affinities.^ 

 By C. A. Barbek. 



Paehytheca was described by Sir J. D. Hooker in 1853, and has, since then, 

 received the attention of many eminent botanists. Two excellent slides have been 

 obtained, and Sir Joseph Hooker requested the author to make drawings and 

 descriptions for publication in the * Annals of Botany,' offering himself to write a 

 general historical and descriptive introduction. The historical portion was read 

 before the Association by the permission of Sir Joseph Hooker, and the author then 

 made a few remarks on the structure exhibited in the two slides. 



There are three zones in the specimens. An outer cortical portion of radiating 

 filaments ; a central portion, consisting of a clear matrix, penetrated in different 

 directions by filaments ; and a zone of spherical bodies separating the cortex from 

 the central part. 



In the cortex the radiating filaments are divided by transverse walls ; there- 

 fore the Alga does not belong to the Siphonese. On the transverse walls are freely 

 developed the callus-Uke thickenings or ' stoppers ' found in OscilUa-ia, Nostoc, &c., 

 and characteristic of the Floridese. The filaments branch in a few cases, and the 

 branching is similar to that of Cladophora : this removes the Alga from the group 

 Cyanophycese. 



In the centre the filaments are also divided by transverse walls. The stoppers 

 and the branching have not yet been observed. 



In tracing the filaments from the cortex, they usually appear to pass between 

 the spherical bodies ; and in one case they appear to arise by branching from 

 one of the spherical bodies. In tracing the filaments from the centre, they appear 

 to enter the spaces between the spherical bodies, and to pass between the bars 

 which are present in these interspaces. 



The large spherical bodies are of dubious nature. In one of the sections, which. 



• Published in full in Annals of Botany. 



