2 BOTANICAL GAZETTE [JULY 
any satisfactory investigation of the process of cell division 
could be made. 
The notion of the middle lamella as the primary cell wall until 
very recently was the most prevalent, and is the one still laid 
down in most text-books of botany. Vines (15) thus states 
this view : 
In the development of a tissue, whether by free cell formation or by cell 
division, septa are formed, that is, walls which are common to contiguous 
cells; these are very thin at first, and appear under the highest magnifying 
power as a simple plate. As the walls increase in thickness and acquire a 
more or less distinctly stratified structure, as seen in transverse section, the 
network of primary septa stands out from the thickening layers proper to 
each cell. The primary septum between any two cells is now distinguished 
as the middle lamella (sometimes also termed intercellular substance); it 
attains a considerable bulk at points where several septa meet at an angle. 
This theory was early stated by Strasburger, and until lately 
he has adhered to it in unmodified:form. In the first edition of 
the Botanisches Practicum (10), on p. 78, he describes a method of 
demonstrating the presence of this median layer in the endosperm 
of the seed of Ornithogalum umbellatum by treatment with sul- 
furic acid, the delicate network of the middle lamella being the 
last part of the cell walls to dissolve. This network, he says, 
corresponds to the original walls present before the process of 
thickening began. In another passage, on page 82, speaking of 
the tracheids of Pinus silvestris, he uses the term “ primary wall,”’ 
which, however, is not the same as the first wall laid down in 
cell division—the middle lamella— but includes the latter as a 
very delicate layer (TZhetlplatte). The middle lamella differs 
from the rest of the primary wall in being “cutinized.” To the 
original partition laid down in the process of cell division, Stras- 
burger (9) had in 1875 given the name ‘‘cell plate.” 
Treub (14), in 1878, studying the living cells of the pro- 
embryo of Orchis latifolia and the ovules of Epipactis palusirs, 
found, after its formation, a splitting of the cell plate, and the 
deposition of a cell wall between the two layers so formed. This 
is, | believe, the first suggestion that the median layer of the 
cell wall is not the plate first laid down in the process of cell 
