402 REVIEWS. 



with the strength of Strasburger's position by the first ex- 

 ample selected — Caulerpa — which happens to be a singularly- 

 fortunate one in many respects, since some of the best ob- 

 servers have investigated and reported upon the structure 

 of its cell- wall. Schacht gave it as affording good examples 

 of growth by apposition. Naegeli, in his large work on starch, 

 stated that an explanation of the course of the layers on the 

 cell-wall and the supporting rods or cords which traverse 

 the cell cavity is not in accordance with the apposition 

 theory. In ' Das Mikroskop' are figures showing (1) how the 

 layers run on the wall and the abutting rod, and (2) how 

 they should run supposing their apposition as layers. Simi- 

 lar views were promulgated by Hofmeister ; but Dippel 

 described the layers as arranged otherwise. In 1880 

 Schmitz pointed out that Naegeli^s description is wrong. 

 The course of the layers is exactly the reverse of that given 

 in the above-named figures. 



Strasburger's description agrees with that of Dippel, and 

 with the latter — Schacht and Schmitz — he regards the course 

 of the layers as explicable oflly by apposition. He points 

 out that the actual state of things is that figured by Naegeli 

 as what should be, supposing the thickening took place by 

 apposition, thus claiming the support of Naegeli himself. 



It appears that the supporting cords which run across the 

 cell cavity, and are perpendicularly attached to the side 

 walls, consist of concentric layers corresponding with those 

 on the walls; that the outer layers of the cord are younger, 

 and run into the innermost and youngest layers of the wall, 

 while the axis of the cord is continued through to the older 

 superficial layers. 



Cords running parallel to the length of the cell often 

 become buried in the thickness of the cell-wall, the layers 

 which are deposited over them becoming bulged towards the 

 lumen of the cell as they pass over ; the layers outside the 

 cord remain flat. 



Explanation of the so-called alternating watery and 

 less watery layers is based on the action of contact surfaces 

 towards the light. Layers may remain separate or become 

 compressed in different degrees. As useful terms, to be con- 

 sistently employed afterwards, Strasburger gives the follow- 

 ing : — Lamella are the primary structures proceeding 

 directly from the protoplasm ; a layer is a complex resulting 

 from several superposed lamellae ; the limiting membrane 

 designates the altered inner edge of a layer. This altera- 

 tion may affect the density of one or more layers, and the 

 thickness of the limiting membrane become considerable. 



