142 Gibson. — Contributions towards a Knowledge 
lishes an important preliminary note (21) on the development 
of the various layers of the stem, in which he claims to show 
a common origin for the so-called pericycle, endodermis, and 
a certain number of the inner layers of the cortex. Each 
endodermal cell, he says, articulates with two cells of the 
pericycle on the one hand, and with two cells of the cortex on 
the other. As Vladescu does not state on which species his 
observations were made, it is necessary to say here that by no 
means all species have their endodermal cells so articulated. 
Indeed, the case varies in the same plant, and it would be 
strange, a priori , if any such arrangement were constant, since, 
according to Vladescu’s own researches, the inner cortex, 
trabeculae, and pericycle are only modified layers of the 
general cortex. Vladescu believes that the endodermis of 
Selaginelta has a conductive function. 
Next in order of publication comes the paper by Dan- 
geard (22) already mentioned. In this memoir the author, 
after briefly reviewing a few of the previously published 
researches, proceeds to discuss the anatomy and histology 
of twenty-eight species of Selaginelta. To this part of his 
work I shall refer later on under the respective species. I 
may say, however, generally, that he gives little or no details 
of the minute structure of the tissue-elements, and the distri- 
bution of the constituents of the phloem is not described save in 
the most casual way. Moreover, these points are not shown 
in his figures, the accuracy of several of which I must call in 
question. In the second part of his paper a comparative 
summary is given of the results obtained, the chief of which 
are as follows : — The epidermis is cuticularized, and the 
lumina of the epidermal cells are often obliterated. The 
conjunctive tissue is differentiated into a ring of stereome, 
a layer of polyhedral cells, and the layers of the inner cortex 
next the lacuna. The endodermal cells are provided with 
cuticularized rings, and are attached by one end to two cells 
of the limiting layer of the vascular cylinder, and by the 
other to two cells of the cortex. He often figures the endo- 
dermal cell as articulating with one cell on either side — his 
