146 M. Mohl on the Growth of Cell- Membrane. 



Mulder now assert that, almost universally, the yet unthickened 

 membrane of young cells, when coloured blue by iodine and sul- 

 phuric acid, is perforated like a sieve by a great number of small 

 pores, through which the light appears bright and uncoloured ; 

 the cells of the pith of Asclepias syriaca, Hoya carnosa, Ricinus 

 communis, of the bark of Euphorbia caput medusa, of the wood of 

 Asclepias syriaca, and Clematis Vitalba, are especially named in 

 relation to this. Harting states that in the old medulla-cells 

 with thickened walls of a great many dicotyledonous trees, e. g. 

 jEsculus Hippocastanum, Syringa vulgaris, Rosa canina, Sophora 

 japonica, there are, among the canals of the dots closed by a 

 membrane, others which are quite open ; and from his investiga- 

 tions he was led to the conclusion that these open pores are not 

 the result of the absorption of the membrane closing the canal, 

 but that they are the remains of the pores occurring in the young 

 cell, which have not, like the others, become closed at a subse- 

 quent period. 



1 confess that to me this statement was unexpected. I had 

 already, in cells I had coloured blue by iodine, often seen very 

 bright dots, which appeared like real orifices, but I always be- 

 lieved that I saw a closing membrane; as I might have been 

 deceived in my earlier observations, I submitted this point to a 

 new investigation. In the first place, however, I must remark 

 that I do not wholly approve of the mode of examination with 

 iodine and sulphuric acid, chosen by Harting and Mulder; a 

 deep blue colouring of the young cell-membrane is indeed ob- 

 tained by this means, but in fact this deep colour is not advan- 

 tageous, as will hereafter appear ; moreover, when too strong an 

 acid is employed a considerable expansion of the cell-membrane 

 is readily caused, by which the dots may be closed; this indeed 

 cannot give rise to a delusion in reference to the presence or ab- 

 sence of a closing membrane, but renders the making of a new 

 preparation necessary. Both evils are avoided when no sulphuric 

 acid is used, but the cell- wall coloured blue by the application 

 of very concentrated tincture of iodine and subsequent moisten- 

 ing with water. In this way we are not exposed to the risk of 

 producing a mechanical alteration of the cell-membrane, and 

 there is the further advantage, that the preparation coloured by 

 iodine may be allowed to dry again, by which means, as is 

 known, the detection of very thin and transparent membrane is 

 especially facilitated. 



I treated in this way the medulla-cells of the young developing 

 bud of Sambucus nigra, Asclepias syriaca, and of the apex of the 

 stem of Euphorbia caput medusa. The result of the microsco- 

 pical examination of these does not at all agree with that offered 

 by Harting and Mulder. It is certainly quite true that the 



