Farmer.— On Isoetes lacustris , Z. 
5i 
histogenic layers at the apex, a calyptro-dermatogen, a double 
cortex or periblem, and a plerome. He practically confirms 
Naegeli and Leitgeb’s previous description, when he says, 
* Das Plerome wachst im wahrsten Sinne des Wortes mit einer 
Scheitelzelle,’ although the investigators just mentioned had 
not apparently foreseen the conclusion to be drawn from their 
own observations. Kienitz-Gerloff 1 * , on the other hand, after 
criticising the views of his predecessors, arrives at the singular 
conclusion that the apex is occupied by an undifferentiated 
meristem : 6 Am naturgemassesten scheint es mir . . . das 
Gewebe der Wurzelspitze von Isoetes als ein vollig indiffe- 
rentes Meristem zu betrachten. In dem durch dieses Meristem 
abgeschiedenen Gewebe sondern sich dann spater die verschie- 
denen Gewebesysteme aus ’ (p. 793). He was probably led 
into this error by confining himself to a study of optical 
sections of cleared apices, otherwise his account can hardly be 
explained at all. His figures do not give the correct relations 
which exist between the different tissues : the derivatives of the 
plerome-initial never appear to run straight down the root, as 
he represents them, except when seen in a plane at right angles 
to that in which it is alone possible to draw any correct 
inference as to their origin. And even some of Bruchmann’s 
figures are open to question on this account. The latter 
investigator does not seem to have paid sufficient attention to 
the stronger roots of older plants, and I find myself unable to 
agree with him in his attempt to draw a sharp line of demar- 
cation between the periblem and the meristem which lies 
externally to it. 
I have invariably found the sharpest distinction to prevail 
between the inner and outer cortex (see PI. V. Figs. 9, 10; PI. 
VI. Fig. 30), while the outer layer of periblem-initials are 
in most cases not clearly separable from the layers giving rise 
to the epidermis and root-cap. The variation which seems 
to exist on this point is suggestive, taken in connection with 
the relation existing between the dermatogen and periblem 
1 Kienitz-Gerloff, Ueber Wachst. u. Zelltheil. und d. Entwickl. d. Embryo von 
Isoetes lacustris , Bot. Zeit. 1881. 
E 2 
