158 HICKS, ON THE DIAMORPHOSIS OF LYNGBYA, ETC. 



tribes of lower vegetable life. This I liave found to bold good in 

 those to whicli 1 have more particularly directed my atten- 

 tion. How far upwai'ds in the vegetable scale the gonidia- 

 prodiicing property is found, I cannot here say, but there is 

 abundant evidence of its existence in mosses. Once gon;dial 

 segmentation having commenced, it may continue for an in- 

 definite time, varying with external influences. Thus, surfaces 

 of considerable extent may, by the continuous segmentation of 

 the terrestial kinds, be covered with growths of cells, hitherto 

 classed together as the Palmellacese. 



Therefore it becomes of importance to determine what are 

 the varieties and limits to this segmentation, and how the 

 linear form of growth can arise from a single cell. This 

 latter process is more difficult to decipher than the change 

 from the linear into the single cell; but it is hoped that the 

 observations whicli follow will tend to throw some light upon 

 it. The facts brought forward below will, I hope, form an 

 apology for so lengthened an introduction to the description 

 of a single plant, inasmuch as the tracing the course of its 

 development brings us to facts bearing on the principles of 

 laws of growth and classification of the lower vegetable tribes. 



The groAvths named in the heading of this communication, 

 have been variously classed : the Lyngbya (Agardh) amongst 

 the Oseillatoriacese ; Schizogonivim, or Bangia (KUtzing), and 

 Prasiola (Meneghini) as genera of Ulvacese. Lyngbya niu- 

 ralis is represented at fig. 1. In its active and normal mature 

 form of growth, it distinctly shows a tubular sheath, of a dia- 

 meter of about -p-p'o-jjth of an inch, containing a number of 

 cells, each with green contents, of a diameter of j g\, p th part 

 of an inch. These contents are generally granular, and in 

 some conditions are disposed, as in many algse, in bands of 

 various forms, leaving colourless spaces between theui (va- 

 cuoles) as at fig. 2. In other stages and conditions the cell- 

 contents are homogeneous, and the septa of the cells are some- 

 times not placed directly transverse, but are more or less 

 curved (fig. 3). Sometimes the contents are absent from one 

 or more cells, either from injuries or other causes ; the 

 cells nearest these on either side' form a rounded end, 

 while the tube or sheath remains healthy. It is not un- 

 usual for such appearances to be present in many parts of 

 one thread, sometimes more or less regularly intermittent. In 

 various modes do these conditions vary, but, in all, the outer- 

 most cell, or even the last two, form rounded ends within the 

 transparent sheath. Thus in many cases, especially where 

 the cell has disappeared, Lyngbya seems to consist of a trans- 

 parent tube containing a number of separated centres of 



