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Daisy G. Scott. 
form the dermatogen. An older stage is shewn at Pig. 8. The 
root-cap is four-layered, but a fifth layer may be noted towards the 
outside, which has a different appearance and has different staining 
properties to the others; this is probably the endodermis of the 
parent stem. The outermost layer of periblem cells is seen to have 
greatly increased in width, a circumstance noted in many of the 
plants examined. 
A transverse section of the young root of about the same age 
as that shewn at Fig. 7 is given in Fig. 9. The central axial row of 
the plerome is surrounded by a single layer of pleromic cells. 
Lying to the outside of this and fitting in between the individual 
cells is the innermost layer of the periblem. Then come four other 
layers of periblem, concentrically arranged, each cell immediately 
behind the corresponding cell of the preceding row, and each row 
containing the same number of cells. Then follow the dermatogen 
and a one-layered root-cap. 
Ruppia. Fig. 10. 
A stage in the development of the root is figured (Fig. 10). 
The plerome cylinder has a single initial cell, and a prominent 
central axial row which cuts off no lateral segments, The pericycle 
has not as yet been differentiated. A single large initial cell gives 
rise to the periblem and the dermatogen. At this stage the root-cap 
is two-layered. 
Naias. Fig. 11. 
A longitudinal section of a young root is shewn at Fig. 11. The 
plerome cylinder appears to arise from two initial cells, though this 
point was not easy of determination. A single initial cell gives rise 
to the periblem and the dermatogen. The root-cap consists at this 
stage of two layers, the cells having a peculiar pentagonal shape not 
seen in any other genera examined. 
Zostera. Figs. 12 and 13. 
A young root is seen in longitudinal section at Fig. 12. The 
root-cap is two-layered. A single initial cell gives rise to the 
plerome cylinder, and a single initial cell, with an undivided segment 
on either side, to the periblem and the dermatogen. 
Fig. 13 shews a young root in transverse section. The 
characters are those described for the preceding figures. 
Van Tieghem does not figure the root apices of Ruppia , Naias 
or Zostera. 
Stratiotes. Figs. 14 and 15. 
A fairly advanced stage is shewn in longitudinal section at Fig. 
