22 Saxelby . — The Origin of the Roots in Lycopodium Setago. 
He states that the roots arise in cells outside the layer next the tracheids, 
before the endodermis is differentiated from the pericambium . 1 
Van Tieghem , 2 on the contrary, asserts that the whole root is formed 
from the true pericycle, which consists of one layer of cells, the outermost 
layer of the plerome of the stem. In this point he finds that the 
Lycopodiaceae agree with all the Phanerogams and with Isoetes, and 
differ from all other Cryptogams, in which the roots are formed from the 
endodermis, or in the case of Selaginella and Equisetum , from layers 
still farther outwards from the plerome. He does not state how he 
distinguishes this pericylic layer in L. inundatum from the endodermis 
before the cell-walls of the latter have become thickened, and Bruchmann, 
in arguing against Van Tieghem’s theory of pericyclic origin of the root, 
refers to the impossibility of distinguishing the pericambium in the still 
meristematic part of the stem. Van Tieghem advances, as proof of the 
pericyclic origin of the root, the occurrence of the endodermis, with 
thickened walls, passing completely round the apex of the root at a stage 
when the three meristematic regions of the root are differentiated, and he 
assumes that the layer within this endodermis is the true pericycle, formed 
from the stem plerome. 
Bruchmann in a figure of a section of L. clavatum , at a stage 
corresponding to that of Van Tieghem’s figure of L. inundatum , marks the 
endodermis stopping short at the sides of a root base, and apparently 
forming the part of the latter nearest to the stem plerome. 3 ’ 4 A section 
like that of Bruchmann might be obtained by cutting the stem at a 
point where the root has broken through the endodermis and is growing 
outwards through the cortex. When the root has reached this stage with 
numerous layers of cells, the exact part played by a layer of cells of the 
stem in the production of the root can scarcely be proved from the 
evidence of continuity of cell-layers. 
Both authors worked chiefly at the same species, namely L. inundatum , 
which seems to differ from L. Selago , firstly in the fact that, in the latter, 
the plerome of the root is formed entirely from that of the stem, and is not 
formed from the same initial layer of cells as the periblem. In the latter 
characteristic it would therefore seem to correspond more nearly to Lemaire’s 
fourth type of root origin . 5 Lemaire worked at the origin of lateral 
roots in Dicotyledons, and came to the conclusion that although as 
a general rule roots arise from the pericycle of the stem, which forms 
all the tissues of the root, other methods of root origin do exist. For 
example, in the case of Asperula odorata the central cylinder of the 
1 Bruchmann ( b ), loc. cit.,p. 75 and following. 2 Van Tieghem, loc. cit., p. 561. 
3 Bruchmann ( b\ loc. cit., Fig. 32, Taf. iv. 4 Van Tieghem, loc. cit., Fig. 582, PI. xl. 
5 Lemaire, Recherches sur l’origine et le developpement des racines lat^rales chez les 
Dicotyledones. Ann. des Sc. Nat., 7 e serie, tome iii, 1886, p. 175. 
