329 



the claims of the spore to be regarded, at least in certain ge- 

 nera, as the analogue of the seed ; and my present object is 

 chiefly to place on record a slight outline of the argument, 

 proposing, at a future time, to return to the subject, and treat 

 it in the detail that its importance deserves. For, however 

 trivial the discussion of such a question may at first sight ap- 

 pear, much depends on our right solution of it. It is like one 

 of the first steps in a chain of reasoning, the wrong determi- 

 nation of which will vitiate all subsequent inferences. If we 

 have incorrect notions respecting the morphology of these 

 vegetables, all our ideas respecting them will be distorted. 



" I shall, on the present occasion, confine myself to some 

 brief remarks on the development of the frond and of the con- 

 ceptacular fruit in the well-known genus Polysiphonia. If 

 we examine a young, growing specimen of any species of this 

 genus, we find that the tips of all its branches terminate in a 

 tuft of dichotomous fibres. The branch consists of a number 

 of cells, placed in a radiating manner like the spokes of a wheel, 

 round a central cavity. Towards the tips of the branches 

 these radiating cells are gradually shorter, and each cell of 

 the last whorl or wheel is prolonged into a dichotomous fibre. 

 T\ii%Jibre never changes its character till it falls away, but the 

 cells (of the branch) below it lengthen and grow wide till they 

 assume their proper form and size. Growth, therefore, takes 

 place below the apical fibre. Such is the case in the primary 

 branches. When a new lateral branch is about to be given 

 off from a primary one, a dichotomous fibre, similar to those 

 at the apex of the old branch, makes its appearance opposite 

 one of the dissepiments of the old branch. Under this fibre 

 a cellular nucleus begins to be formed, which increases in size, 

 and takes the character of one of the branches, new fibres being 

 developed upon it as it acquires complexity. As such fibres 

 are constantly met with on all the groiving apices while the 

 frond is in process of extension, it is not unnatural to suppose 

 that they are actively concerned in the development they ac- 



