MICROSCOPICAL MEMORANDA. 221 



tions of woody tissue imbedded in other tissue, apparently of plants much 

 lower in their organization. He had also detected traces of structure 

 in the ashes of anthracitic coal received from Sir H. De la Beche. Mr. 

 Phillips considered this evidence rather in favour of the view that coal 

 was in a great measure formed by plants growing on the spot, and not 

 by drifting ; the evidence of such drifting was formerly much stronger 

 impressed upon his mind ; but he had met with many phenomena, and 

 this amongst them, which tended very much to diminish the force of his 

 former conclusions. Athenceum, July \Qth, 1842. 



Hassall on the Growth of the Conferva . The rapidity of the growth 

 of most species of Conferva, has been a subject of surprise to many ob- 

 servers of nature, and the explanation which 1 am about to offer of the 

 causes of this very rapid growth, has not, that I am aware of, been 

 before noticed. Most, if not all, the Conferva appear to me to increase 

 in two ways : first, by the continued growth of the free extremities of 

 the different filaments ; this method is obvious, and need not be in- 

 sisted on. Secondly, by the repeated growth and subdivision of each 

 cell entering into the formation of the filaments. I long suspected the 

 existence of this mode of development, but was first convinced of its 

 reality by an examination of those species of the genus Conjugata of 

 Vaucher, distinguished by the presence of spiral tubes winding round 

 the interior of the cells, and especially of the one named Conjugata 

 princeps. If the filaments of this species be carefully examined and 

 contrasted together, it will be seen, that in some the length of the cells 

 only just exceeds their diameter, and that each cell contains three spiral 

 tubes, which together perform from seven to eight turns in each, the 

 coils almost touching each other ; that in others the length of the cells 

 is more than three times the diameter, but that still each cell contains 

 only the same number of spiral turns, viz. seven or eight, which now, 

 instead of being nearly in opposition, are widely separated, thus plainly 

 proving the elongated cells to be derived from the growth of the shortest 

 ones. And again, it will be noticed in others, that the cells have re- 

 turned to their original length, but that each now contains only three 

 or four spiral turns, thus manifestly proving the division of the elon- 

 gated cell, and completing the chain of evidence which establishes to 

 demonstration the existence of the mode of growth to which I have 

 referred in the section of the genus alluded to. The number of spiral 

 tubes varies in this and other species in different filaments, but not in 

 the same : and this makes a corresponding difference in the length of 

 the joints or cells, which are longer if there be four or five tubes instead 

 of three. The proofs now to be adduced, that this mode of growth like- 

 wise takes place in all Conferva which are composed of simple un- 

 branched filaments, a large class, are little less conclusive than those 

 first commenced. In most of the filaments of these, the cells will be 

 observed to be of various lengths, some twice as long as others, and 

 these again of very intermediate length. Now, by means of this law of 

 growth, this variation in the length of the cells is at once and satisfac- 

 torily accounted for, which is not to be done in any other way. But 

 this is not all : the progress of the formation of the septa which divide 



