Notes. 
181 
of the Pontederiaceae are not fixed, and the object of this note is to 
show the connection between the different appearances which they 
may exhibit in longitudinal section. 
If transverse sections are made through a node of Eichhornia 
azurea, Kunth, or E. crassipes , Mart., on which adventitious roots 
are not yet visible, one is pretty sure to get some longitudinal sections 
of young roots still enclosed in the tissue of the stem. They do not 
come out from the stem quite horizontally, but as a rule there are 
a few of them cut nearly in a median plane in their apical portion. 
These show, when treated in the above-mentioned ways, that even in 
the youngest stages it is quite impossible to refer the rootcap to the 
same initials which give rise to the dermatogen and periblem. There 
is a distinct calyptrogen layer 
(Fig. 4, c) dividing by peri- 
clinal, rarely by anticlinal, 
walls. Other periclinal 
walls are not formed in 
the calyptra, but here and 
there anticlinal walls may 
be formed in other layers. 
Between the calyptrogen 
and the plerome there is 
only one layer of cells, 
giving rise to both der- 
matogen and periblem 
(Fig. 4, z), and besides 
there are distinct initials 
for the plerome. In short, 
the young adventitious roots 
of the Pontederiaceae have 
very much the same structure as the primary roots of Pontederia 
cor data , and belong therefore to the type of the Gramineae. 
The number of cells forming the initial layer of the periblem and 
dermatogen varies from two to four (in longitudinal section) in the 
roots at the stage I have described, but if roots are examined when they 
have just broken through the tissue of the stem, the number of cells is 
fewer, often only one cell being seen undivided. At a further stage of 
development the dermatogen becomes quite independent, and extends 
Fig. 4. Eichhornia azurea , Kunth.— Median 
longitudinal section of the apex of an adventi- 
tious root while still enclosed in the tissue of the 
stem : pi plerome ; pe periblem ; d dermatogen ; 
cal calyptra ; c cells of the calyptrogen ; i initials 
of the dermatogen and periblem. 
