MoLLET. — On the Structure of Hormosira billardieri. 319 



nodes, but frequently from the nodes themselves. It may be dichotomous 

 (PL XIV., figs. 6 and 7), polychotomous (PI. XIV., fig. 8), or take the form 

 of a lateral shoot (PL XIV., fig. 9), in the same manner as the internode 

 mentioned above. 



The plants used in this investigation received no chemical preparation 

 whatever ; they were gathered in the living state, and left to dry for some 

 days, after which time they were in a firmer and better condition for 

 making thin sections than when freshly gathered. If kept, however, too 

 long in a very di-y atmosphere they showed a great tendency to brittleness, 

 in which state they were very difficult to cut. 



Before proceeding to the detailed structure of the plant, I would also 

 mention that I have adhered to Hooker's nomenclature in regard to the 

 terms node and internode. A node is generally looked upon as that part of 

 the plant from which branches or leaves arise ; but, in this case, the 

 secondary stems generally branch out from the inflated internodes (see pre- 

 vious remarks on branching), which are therefore incorrectly named. 



Nodes. — The nodes, which are solid throughout, consist externally of a 

 single layer of thin polygonal cells (PL XIII., fig. 1), somewhat resembling 

 the ejpidermis of the Phanerogamia, but unlike the latter are in a living 

 state, many being found in the process of division. These cells, though very 

 irregular in outline, are mostly hexagonal, and are so easily separated from 

 the limiting tissue beneath, that in most of the sections made fragments of 

 the tissue which they go to form were continually seen. This layer appears 

 to be absent in the species of Puci examined by Mr. F. 0. Bower,* as he in 

 no place mentions its existence. 



The layer of tissue next beneath is composed of minute oblong cells, 

 gradually increasing in size as they recede from the external tissue. To- 

 wards the surface these cells are oblong, but they become more oval-shaped 

 towards the inner tissues. (PL XIII., figs. 2 and 3.) It is only in very 

 thin sections that the shape of these cells — the granular contents of which 

 are deeply colom-ed with chlorophyll — can be satisfactorily determined ; in 

 thicker ones they appear to be of much greater length than is really the 

 case. This layer corresponds with the "limiting tissue " of F. 0. Bower. 



The tissue adjoining on the inner side, his cortical tissue, is an aggrega- 

 tion of irregularly-shaped cells, containing small quantities of chlorophyll, 

 and having no clearly-defined division between the cell-walls (PL XIII., 

 figs. 2 and 8). This layer graduates from the limiting tissue on the 

 outside into a mass of parallel cells, forming the central part of the node 

 (PL XIII., figs. 2 and 3). 



* On the Development of the Conceptacle of the Fucaces. (" Quart. Journ. Micro. 

 Science," January, 1880.) 



