18 Mr. G. H. K. Thwaites on the Cell-Membrane of Plants. 



common Conferva glomerata. In this species the cells are ex- 

 tremely large, and the endochrome is in considerable quantity ; 

 and the cells apparently continue increasing in size during the 

 whole period of their vitality, so that those at the base of the 

 plant are larger than those recently developed. Some species of 

 Conferva consist only of single unbranched filaments, so that, in 

 these, new cells are added only at one point \ but in the species 

 under consideration new cells originate from every part of the 

 plant, and thus we have a favourable opportunity of observing 

 what takes place when a new cell is being produced from one 

 which has been some time developed. A slight protuberance is 

 observed upon the cell-membrane, which has the appearance of 

 being caused by the enlarged contained endochrome endeavour- 

 ing to force its way out of the cell. This protuberance increases 

 at the same time with an increase of the endochrome, and be- 

 comes of some considerable length before there is any appearance 

 of a septum dividing it from the original cell. The endochrome, 

 however, subsequently divides, and a membrane is developed over 

 each of the divided ends ; or, what is the probable explanation, 

 a development of cell-membrane has been taking place during 

 the whole process, and, still going on, a membrane is now natu- 

 rally formed over those ends of the endochrome where the pre- 

 vious continuity has been broken. That an addition is continually 

 being made to the cell-wall is evident, since there is no other way 

 of accounting for the increasing size of the cell and thickness of 

 its membrane. 



An abnormal growth which sometimes takes place in the cells 

 or long tubes of Vaucheria will serve well to illustrate how im- 

 mediately an increased production of cell-membrane is consequent 

 upon an additional development of endochrome. The cells of 

 Vaucheria are occasionally found to be infested with a species of 

 Vorticella, an infusory animalcule. This little animal is seen 

 occupying large pear-shaped protuberances upon the frond of 

 Vaucheria, in which it deposits its ova. Now it is interesting to 

 observe the mode in which these peculiar protuberances are 

 formed. The Vorticella may, in some instances, be seen within 

 the tube of the plant, and from the slight alteration in the endo- 

 chrome, it may be inferred that the little animal has not been 

 long present there ; in other cases it may be observed that the 

 presence of the Vorticella has caused an evident dilatation of the 

 cylinder of endochrome with a corresponding enlargement of the 

 cell-membrane ; whilst in other examples this dilatation has gone 

 on so as to have produced a large pear-shaped appendage to the 

 frond, within which the Vorticella may be seen moving. But 

 what I would wish particularly to draw attention to is the fact 

 that the stimulus arising from the presence of the Vorticella has 



