146 PRINGSHEIM ON THE STRUCTURE 



layer" into the cell-wall takes place when the former has 

 reached the highest stage of formation — that is to say — when 

 it constitutes a complete parietal investment. The primordial 

 utricle might, v^ery readily, be taken for a membrane, but it is 

 not a membrane distinct from the cell-wall, being merely its 

 youngest cellulose layer, whose reaction with iodine depends 

 upon the svibstances still adhering to it, since it is impossible 

 that should bo pure at this time. Usually it is only the 

 outermost portion of the " cutaneous layer " which is inti- 

 mately applied to the contiguous cell-wall, w^hilst the inner 

 portion is gradually perfected, and eventually comes to be 

 deposited in the same way. This just formed, youngest cell- 

 layer also constitutes the folds which advance so as to effect 

 a complete constriction in the interior of the cell. But it 

 occasionally also happens that the innermost part of the 

 "cutaneous layer" becomes a young cell-wall, in which case 

 the outer portion is left enclosed between layers of cell-wall. 

 In this way is produced the so-termed "jelly " in the Palmel- 

 laceae, and the cellulose ring in (Edogonium. All these 

 formations are merely slight modifications of cellulose, which, 

 on the addition of acids, is either rendered blue by iodine, or 

 is converted into a soluble compound belonging to the amyloid 

 series, and which is not coloured blue by sulphuric acid and 

 iodine. Consequently, when the latter phenomenon is not 

 manifested in a membrane, the absence of cellulose cannot 

 absolutely be assumed. 



The mode of division of the parent-cells of the pollen is 

 discussed in the fifth section. After giving a historical sum- 

 mary of previous observations on the subject, the author states 

 the results of his own researches in Allium Victorialis and 

 Althcea rosea, in which he finds precisely the same conditions 

 to obtain as exist in the Algce. The formation of the septum 

 is similar, except that in this case it becomes thickened before 

 it is completely closed. 



The sixth section is entitled " Nature of the cell-division 

 in plants." In this chapter the author shows that the capa- 

 bility possessed by the cell-wall of forming folds which are 

 thrown out towards the interior is a general property of that 

 tissue, and consequently that the act of division consists in 

 the advancement of this plication till a complete constriction 

 is effected. 



In the seventh section it is shown that the free formation 

 of cells consists in this : that the contents alone take part in 

 tlie formation of the secondary cells, the membrane of the 

 parent-cell having no share in it. But connected with this, 

 various cases occur, which are more particularly specified by 



