1 82 Notes. 
right round the apex, and thus two layers of cells are now seen 
between the calyptra and 
plerome (Fig. 5). I am not 
able to state at what age 
this final differentiation is 
effected ; it seems to me to 
vary according to the con- 
ditions under which the 
roots grow, though I cannot 
exactly say what these con- 
ditions are. 
As the roots have thus 
acquired the apical structure 
of Pisiia and Hydrocharis , 
it might be supposed that 
their final differentiation is 
due to the disappearance 
of the calyptrogen layer, 
or rather to its inactivity, 
as happens in those genera ; 
but this is not the case. Sometimes the rootcap dies off completely, 
and then it is quickly followed by the other parts of the apex, but 
usually the calyptrogen seems to be active as long as the apex is 
growing, though the rootcap, which grows very slowly, can be easily 
detached even in comparatively young roots. It certainly cannot be 
accidental that all the plants in which the most differentiated apical 
meristem of the roots has been found are monocotyledonous water- 
plants, and it may be noted that Holle 1 has found in Vallisneria a 
transition from the type of the Gramineae into the type of Hydro- 
charts and Pistia , just as I have observed it in Eichhornia crassipes 
and E. azurea. 
I have still to add that the apical meristem of the rootlets in fairly 
advanced stages corresponds, as far as I have observed, with the type 
of the Gramineae, and Nageli and Leitgeb’s figure 5 cannot therefore 
represent a median section and satisfactorily illustrate the structure of 
a rootlet. 
SELMAR SCHONLAND, Oxford. 
Fig. 5. Eichhornia azurea , Kunth. — Median 
longitudinal section of the apex of an old ad- 
ventitious root : pi plerome ; pe periblem ; d 
dermatogen ; cal calyptra ; c calyptrogen ; i x 
initials of the periblem (the cell to the right 
of the three lettered cells is also an initial) ; 
i 2 initials of the dermatogen. 
1 Bot. Zeitung, 1877, p. 542. 
