404 BOTANICAL GAZETTE [DECEMBER 
origin of stelar structures, for, unlike most of his countrymen, 
he has always been willing to admit that there is some evidence as 
to the extrastelar origin of the pith in certain instances. To him 
belongs the credit of having called attention to the fact that in 
certain of the ferns, structures which are unquestionably extra- 
stelar in their origin may penetrate the central cylinder of the stem. 
Fig. 1 of the plate accompanying this article shows a transverse 
section of the stem of Onoclea (Struthiopteris) germanica. The 
stem is very irregular in outline on account of the crowded leaf 
bases attached to its surface. The leaf bases, actual or potential, 
are distinguishable by the fact that they have a double fibro- 
vascular bundle. In the substance of the stem lie a number of 
cavities, situated for the most part within the boundaries of the 
central cylinder, as determined by a line drawn external to its 
bundles. These cavities are more or less occupied with a filmy 
substance representing the ramental covering of the epidermis. 
By inspection of the figure it can be clearly made out that the 
cavities plugged with ramentum, occurring in the substance of the 
pith, are derived from outside, and represent ingrowths of the 
external epidermis, including the outside air. Fig. 2 represents a 
part of a similar section somewhat more highly magnified. On 
the left may be seen the communication of the medullary pocket 
with the exterior surface of the stem. It is an axiom with the 
greater number of the English anatomists, that if pockets or 
apparent ingrowths of tissues, normally extrastelar, occur within 
the central cylinder, these are not what they appear to be, namely, 
incursions of extrastelar tissues into the substance of the stele, 
but, on the contrary, are merely portions of the stele which have 
been so transformed as to resemble tissues of the cortex. In the 
case supplied by our two figures we have a logical reductio ad 
absurdum of the usual English view, for here we have not only 
the external hairy covering of the stem but even the outside air 
making their way into the innermost sanctity of the stele. Even 
the most convinced adherent of the stelar origin of the pith must 
admit that in this case structures which are quite outside the stele 
4 GwynNE-VAucHan, D. T., On the possible existence of a fern stem having the 
form of a lattice-work tube. New Phytol. 4:no. 9. 1905. 
