EESEAROHES ON PROTOPLASMIC CONTINTTITY. 317 



closing membrane. For instance, on page 9 he observes "short 

 threads crossing from one side of the membrane (i.e. the mem- 

 brane of the cell wall bordering a gap) to the other;" and 

 again, page 17, " a somewhat stouter and more strongly refrac- 

 tive thread not unfrequently unites the portions of membrane 

 bordering the gap in a bridge-like manner, and crosses the 

 threads which pass through it." On page 111 may quote a 

 passage which shows the want of accuracy in his botanical 

 terminology, for he describes as middle lamella " the layers 

 immediately below the cuticle, which are double or three 

 times as thick as the partition walls between the epidermal 

 cells.'' 



The last point I have to deal with is the question of the 

 perforation of the cell wall, and the possibility of following 

 protoplasmic structures into its substance. TangP has shown 

 that it is impossible to see anything of the protoplasmic threads 

 in the cell walls of the endosperm cells of Strychnos, 

 Phoenix, and Areca, by direct observation in such fluids as 

 dilute glycerine, and even by ordinary staining. In each 

 case a special mode of preparation must be employed. I can 

 fully bear out his statements, and, indeed, in some of my 

 most striking examples of the occurrence of protoplasmic 

 filaments in the cell wall, it was quite impossible to see any- 

 thing of them when examined in the usual manner. I was 

 unable to observe anything of the kind in the epidermal cells 

 of Dracaena and Rhododendron, but I think that some 

 satisfactory explanation can be given of the appearances which 

 Professor Frommann describes. If sections of Dracaena be 

 examined in dilute glycerine, what appears to be a reticulate 

 structure can be distinctly observed, both on the upper, and the 

 side walls of the epidermal cells. The outlines of the walls 

 bounding the cell lumen are not well defined, and, as Professor 

 Frommann says, the protoplasm seems to gradually merge, as 

 it were, into the cell wall, as he endeavours to represent in 

 fig. 25, plate I. Indeed, the whole appearance is most striking. 

 If, however, excessively thin and exactly transverse sections 

 ' Pringsheim, ' Jalir.,' 1. c. 



