Farmer. — On Isoetes lacnstris, L. 53 
investigate this point independently, although the statements 
made in reference to it by Van Tieghem and Douliot 1 leave 
the matter in some doubt. I cannot, however, agree with 
these authors in regarding the cortex of the root as referable 
to a single layer of periblem-cells, nor do I find their figure 
(PL XL. Fig. 583) at all convincing. It does not represent 
anything like that which I have seen in perfectly median sec- 
tions where the distinctions of the different tissues are much 
more clearly marked than in their figure, in which the plerome 
is very much larger in proportion to the size of the whole root 
than in any preparation I have met with. 
I have been unable to follow out all the stages of the 
dichotomy of the root, but so far as my observations extend, 
they confirm Bruchmann’s statements on these points. 
As regards the exogenous character of the primary root 
my results are, in the main, in agreement with those of other 
writers ; the first divisions certainly occur in the superficial 
layer of cells, and the inner of the two daughter-layers formed 
by this periclinal division again divides, giving off fresh root- 
cap-cells at its exterior. The inner meristems are, however, 
formed from cells within this layer, which only forms the outer 
cortex, as is partly indicated in PI. V. Figs. 2, 3 ; and Kienitz- 
Gerloff also has arrived at the same result. The outer layers of 
the root are as a matter of fact exfoliated, and relying on this 
fact, the author just cited argues against the claims of the root 
to be regarded as exogenous. The difference between exogeny 
and endogeny in a structure such as this is, however, some- 
what shadowy, and perhaps it would be well to regard it as 
representing actually a transition between the two. Of course 
many (comparatively speaking) exogenous roots are now 
known, amongst which may be quoted that of Phylloglossum. 
Van Tieghem and Douliot have attempted to correlate the 
relative time of development with the exo- or endo-geny, but 
I think that the instance of Isoetes shows that this principle, 
useful as it is in many cases, may be carried too far. The root 
1 Recherches comparatives sur Forigine des membres endogenes dans les plantes 
vasculaires, An. Sci. Nat. (Bot.) 1888. 
