124 Daisy G. Scott. 
to it develops a “digestive sac” of greater or less thickness, and that 
this envelopes the root up to the time of its exit. In the present 
investigation neither the origin from the pericyclic cells nor the 
endodermis forming a “digestive sac” were traced; moreover, the 
pericycle and the endodermis of the parent stem could not be 
distinguished as differentiated layers. One section figured, however, 
that of a fairly young root of Vallisneria (Fig. 8) shews what appears 
to be a layer outside those formed by the calyptrogen, which differs 
in size and colour and has no common origin with the outer layers 
of the root-cap. This, perhaps, arises from the endodermis of the 
stem. In Vallisneria the central tissue of the stem appears to be 
more clearly marked off from the cortex than in others examined- 
Van Tieghem traces the roots from the division of two or three 
cells of the “rhizogenic arc” of the pericycle, which by one 
tangential division cut off the central cylinder and by a second 
tangential division exterior to the first cut off the cortex. The 
cells at the base of the cortex of the root are called by Van Tieghem 
the “ epistele,” and are formed, he considers, from the lateral 
cells of the “ rhizogenic arc,” and not from the central cell which 
cuts off the cells which become the initials of the plerome, the 
periblem and the root-cap, and so are not covered at the base, at 
any rate when older, by the root-cap or the dermatogen. 
In the present investigations the junction of the base of the 
root with the stem was not clearly marked, but Van TieghenTs 
“ epistele ” was certainly not observed ; the cells at the base of the 
cortex of the lateral roots appeared to merge into those of the 
cortex of the stem. 
II.— Apical Meristem and the Initial Groups. 
In the plants examined three sets of initial cell-groups were 
distinguished, giving rise respectively to (1) the plerome, (2) the 
periblem and dermatogen together, (3) the calyptrogen. Now 
Janczewski (3), according to De Bary, finds in most of the roots of 
Monocotyledons these same three sets of initials, and among those 
plants he examined those also investigated in this paper, areAlisina 
and Stratiotes. Treub (4) (according to De Bary) for the most 
part confirms Janczewski, mentioning especially Liinnocharis and 
Stratiotes. In some plants, however, among them Alisma and 
Bntoinus , he says there is a common group of initial cells, two layers 
thick, from which the root-cap, the dermatogen and the periblem 
arise. This is contrary to the results obtained in the present 
investigation. 
