REVIEWS. 403 



By behaviour on swelling, optical characters, and action 

 towards reagents, the cell-wall betrays the presence of 

 layers, variously altered by compression, &c. ; the gradual 

 entrapping and burying of substances in the successive 

 layers demonstrates the apposition of the latter. After re- 

 ferring to further details Strasburger proceeds to describe 

 the origin of the young supporting cords. 



In the apex of the "Rhizome" of Caulerpa is much dense 

 protoplasm, in which starch and fine granules are distri- 

 buted; certain granules distributed over the surface of the 

 cell-wall, and in strings of protoplasm proceeding from this, 

 are to be distinguished as giving proteid reactions, «&c. ; 

 these " microsomes," arranged on the very fine strings 

 which give rise to the supporting cords, remind one of the 

 optical section of a cell-plate just before the membrane is 

 formed. 



As will be seen later, Strasburger considers the ^' micro- 

 somes ^' as elements derived from the protoplasm to form 

 the cell-wall. In the above case they are to be regarded as 

 brought by streams in the protoplasm to the inner surface 

 of the cell-wall, and to the outside of the young cord ; here 

 they become arranged into series, and plastered on — so to 

 speak — as " lamellee." 



In young growing internodes of Clematis the pith cells 

 are bounded by simple thin walls, which give a blue re- 

 action in zinc-chloride and iodine ; only at the intercellular 

 spaces do they appear separable into two layers. In the 

 next lower internode this primary cell-wall has a thick- 

 ening layer deposited over its inner surface, and separated 

 by a very delicate line from the former ; this thickening 

 layer gives the reaction of pure cellulose, but the primary 

 wall has already become cuticularised, and resists acid. 



The succeeding internodes have the pith cells thickened 

 by further deposits of similar layers as Dippel described. 

 When older, the outer layers become slightly changed ; but 

 faint *' separation surfaces " mark them. These separation 

 surfaces are of the nature of '' limiting membranes," and 

 appear to be due to the continued action of the surrounding 

 medium during pauses in the apposition of the layers which 

 they separate. In the layers themselves can be seen indi- 

 cations of lamellge. Careful treatment with H2SO4 shows 

 that the cellulose layers dissolve more rapidly than the 

 slightly altered limiting membranes, and at length a net- 

 work of middle lamellae — the altered original walls — alone 

 remain. The walls of the older pith cells of Clematis are 

 pitted, and Strasburger shows that the pit arises by arrest 



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