76 
F. 0. BOWER. 
were subjected to severe criticisms by Sachs at the opening of 
the second memoir of the above-mentioned series (1. c., p. 48). 
Thus, practically, the ground was clear for the latter author. 
How well he drew together and systematised the whole sub- 
ject of the structure of meristems will be already familiar to 
most botanists. It may be safely stated that no work has given 
a greater stimulus to the study of meristematic tissues than 
this of Professor Sachs. 
One of the most important points brought forward by Sachs 
is that the arrangement of the walls in such organs as grow 
with a single apical cell may be shown to fall under a similar 
system of construction to that of similar organs in which no 
apical cell can be distinguished. He has formulated this in 
the proposition that the apical cell “ is merely a gap in the 
system of construction of the punctum vegetationis, that 
is, the apical cell is that point in the embryonic tissue in which 
as yet no anti- or periclinal walls, nor any radial longitudinal 
walls have been formed” ( f Vorlesungen/ p.555). This view 
of the matter affords a bridge connecting those types which 
grow with a single apical cell with those having a small-celled 
primary meristem, and as a necessary result draws closer atten- 
tion to those which may be regarded as transitional types 
between the structure which is, roughly speaking, characteristic 
of the lower forms, where an apical cell is present, and that 
more typical of the higher plants, viz. with a small-celled me- 
ristem. Such intermediate types had already been described 
in various examples, both of roots and stems, in which the 
whole tissue of the organ, instead of being referable in its 
origin to a single apical cell, is derived from two or more 
initial cells. As examples may be cited the roots of the 
Marattiaceae, first investigated by Russow (‘Yergl. Unters./ 
pp. 107 — 109), but subsequently, and apparently with more 
exactitude, by Schwendener (‘ Sitz. d. k. Preuss. Akad. d. 
Wiss./ 1882, p. 183). According to the latter author, there 
are in this case four oblong initial cells in juxtaposition ; with 
the exception of the sides in contact with the other initial 
cells, segments are cut off from all the sides of these cells ; 
