Mr. G. H. K. Thwaites on the Cell-Membrane of Plants. 19 



been operating immediately upon the internal surface of the cy- 

 linder of endochrome, causing an abnormal development of this, 

 accompanying and consequent upon which has been a correspond- 

 ing and regular development of cell-membrane ; showing that the 

 amount of production of cell-membrane is regulated by the growth 

 of the endochrome. 



I will now proceed to make a few remarks upon a structure 

 which is developed in greater or less amount in most Algae, — ex- 

 ternal to the cell-membrane, — possessing some characters in com- 

 mon with it, and probably in many cases performing a similar 

 office in the oeconomy of the organism. The structure I allude 

 to is the mucus which surrounds the cells of Algse, and in some 

 species, such as in many of the Palmellece, of considerable extent, 

 so as to make up by far the greater part of the plant. In some 

 of the Palmellece indeed, the plant at first sight appears to be 

 composed of an amorphous gelatinous mass, containing cells im- 

 bedded in it, and would lead to the idea that this gelatinous mass 

 is the matrix from which the cells are developed, and to which 

 they owe their origin ; but such is really not the fact. There are 

 some species of PalmellecE which show the character of this mucus 

 very clearly, and in which its development can be traced without 

 difficulty. In Coccochloris cystifera, H assail, a species not un- 

 common in the neighbourhood of Bristol on rocks and walls, may 

 be readily observed the circumstances under which the mucus is 

 developed, and that this mucus is of definite form and quantity. 

 This species of Alga, like most if not all the Palmellece, increases 

 not only by an enlargement of its cells and the ordinary repro- 

 duction of these from a parent cell or spore, but during the de- 

 velopment of the plant the number of cells is very much increased 

 by fissiparous division — each cell becoming divided into two or 

 four — no doubt in the same way as occurs in Zygnema, Isthmia, 

 &c. Now if the plant, in which this process is going on, be 

 carefully examined, it will be seen that the mucus is developed 

 in definite quantity around each cell and doubtless by it. For 

 we may perceive one cell in which there is no indication of fissi- 

 parous division ; another in which this process has just taken 

 place, but the cells are yet in close apposition ; another in which 

 the two new cells are separated to some distance from each other ; 

 and if we examine into what has led to their separation, we may 

 find that this arises from a definite development of mucus around 

 each of them and within the mucous envelope of the original cell ; 

 and lastly, we may find a pair of new cells of nearly equal size 

 with the original one, each with nearly the ordinary amount of 

 gelatine or mucus surrounding it, and the mucous sheath of the 

 original cell nearly absorbed. In a Palmella found in Sussex by 

 Mr. Jenner and sent me by Mr. llalfs under the name of P. hya- 



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