26 Sccxelby . — The Origin of the Roots in Lycopodium Selago. 
plates were found on the walls of such cells. These cells become shorter 
and rounded in the region of the root base, and the nuclei also become 
rounded. In this and other vertical sections the outermost layer of these 
cells is seen to be continuous with the periblem of the root base, i. e. the 
second layer from the outside of the base. The dermatogen is continuous 
with the innermost layer of cells which are without the narrow elongate 
nuclei, and since these cells are also wider, it may be concluded they are 
cortical in origin. 
The Growth of the Roots. 
Bruchmann favours the view that there are four distinct histogenous 
layers in the roots of Lycopodiaceae, while Van Tieghem is of the opinion 
that there are only three. Van Tieghem in this point follows Strasburger. 
The answer to the question depends on the method of formation of the 
root-cap. Van Tieghem 1 states that the cap is formed from the epidermis, 
which may become from twelve to fifteen layers thick. Strasburger 2 is of 
the opinion that the calyptrogen is formed in the first place from the 
dermatogen, but at once begins to divide tangentially and radially, inde- 
pendently from the latter. Bruchmann, on the contrary, in his earlier work, 
in which he enters more especially into the question of root origin, and 
again in his second treatise, says that formation of the root-cap by tangential 
division of the dermatogen seldom occurs, but in most cases an independent 
calyptrogen is formed. 3 In L. Selago I find the dermatogen soon divides 
tangentially two or three times, the first divisions being at the sides, not in 
the centre of the apex. The cells cut off on the outside form the root-cap 
seen in all but the youngest roots. These cells digest and absorb the 
surrounding cells of the cortex, leaving a way clear for the root to pass 
through. In vertical sections through the root apex, as for example in 
Fig. 6, the cap is seen to consist of three or four rows of cells arranged 
in radial lines corresponding with dermatogen cells. The cells of each row 
increase in size from the periblem to the apex of the root-cap. This seems 
to me to be evidence in favour of the view that there is no definite 
calyptrogen, that is, that there are only three meristematic layers in the root. 
At a later stage than that represented in Fig. 5, several of the cells 
in the region of the apex divide together in the periblem, at first tan- 
gentially, forming two or three layers of cells, then radially. As many as 
four rows of periblem cells were seen at the centre of the apex in some 
roots still in the cortex. The cells of the plerome, on the contrary, divide 
1 Van Tieghem, loc. cit., p. 554-5. 
2 Strasburger (a), Das Bot. Pract., 2nd ed., 1887, pp. 59, 60; and (b) Conif. u. Gnet., 1. Aufl., 
Jena, 1872, p. 355, Fig. 32, Taf. xxv. 
3 Bruchmann ( b ), loc. cit., p. 71-2. See also for further references Nageli u. Leitgeb, and 
Reinke. 
