The Stelar Theory. 14 i 
genuine insight into, the problems dealt with, which is sufficiently 
uncommon in our days. In fact, the author exhibits the powers 
not only of a careful observer of detail, but also of a capable 
generalizer on the broader issues at stake. 
The book is divided into two parts of which the first deals with 
“The Stelar Thery and the History of Development [Ontogeny] ” 
and the second with “The Stelar Theory and Comdarative Anatomy.” 
The first chapter is entitled “ Facts connected with the differ¬ 
entiation of tissue into dermatogen, peribleni and plerome," and con¬ 
tains a critical discussion of the literature on the subject. The 
author concludes that Hanstein’s primary divisions of the tissue 
are inconstant, and often obscure, irregular or almost absent in the 
embryo of Phanerogams, and altogether wanting in that of the 
Vascular Cryptogams; they are equally absent in the apical 
meristem of the latter group. As regards the Phanerogams, 
although in some cases the apical differentiation of the stem is clear 
and sharp, yet in other cases this is by no means the case; so that, 
consequently, much importance cannot be attached to the Hanstein 
division. It is, however, more constant in the root. The tissues of 
lateral organs do not arise from the corresponding tissues of the 
organs bearing them. Chapter 2 is headed: “The Correspondence 
between the Primary Tissues of Hanstein and these of Van 
Tiegham,” and its object is to determine whether the dermatogen, 
periblemand plerome of the apical region give rise respectively to 
the epidermis, cortex and central cylinder of the lower (mature) part 
of the stem. The following are his conclusions, founded on original 
observations. In those roots where, at the apex, there exists a sharp 
division between peribleni and plerome, the cortex arises from the 
former and the central cylinder fi oni the latter. In stems, on the 
contrary, and in the only case in which the apical divisions were 
regular, viz., in Hippuris, this correspondence fails to obtain,.for in 
this plant the endoderniis (“ Schutzscheide”) arises, along with a 
few cortical layers, from the plerome. In those roots in which the 
cell-divisions do not take place so regularly, there is found, as in the 
great majority of stems, absolutely no correspondence between the 
apical differentiation and Van Tieghem’s division. In view, there-, 
fore, of the fact that the Hanstein division of the tissues holds 
good only for a few roots and for one single stem, the idea that 
that division can be of any phylogenetic and morphological impor¬ 
tance must be rejected. Even the dermatogen does not always 
correspond to the epidermis, though it much more frequently gives 
rise to the latter than do peribleni and plerome to the cortex and 
central cylinder respectively. As inaugurating the second part of the 
book, chapter 3 treats of “The Limit between Cortex and Central 
Cylinder in Stems” of the three great classes of Phanerogams. In 
Gymnosperms no definite endoderniis exists, but nevertheless a 
sharp actual distinction obtains between cortex and central cylinder. 
In Monocotyledons a nionostelic structure with clearly-differentiated 
endoderniis is very frequent. In some stems, however, a limit 
between the two main tissues cannot be made out; in others this 
limit is obvious, but a specialised sheath does not exist. Yet, as all 
Monocotyledonous stems agree in their general structure, the main 
divisions of Van Tiegheni will apply, in spite of certain variations, 
to all cases. As regards Dicotyledons the distinction between 
