638 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
They were found in sixteen out of the thirty-eight species examined, 
presenting the appearance of black shining exceedingly narrow threads 
varying greatly in size, between 0 • 4 and 18 mm. in length and between 
0 * 06 and 0 * 35 mm. in thickness. In almost all cases the cells from 
which the fundamental tissue and the supporting bundle originate were 
found to be uniform in size and form ; in only two species ( Pteris 
aquilina and Oleandra hirtella) was there a differentiation of the elements 
of the primary meristem. With the appearance of the brown substance 
the merismatic power of the cells ceases. The cells become at a late 
period periodically filled with starch, like the surrounding parenchyma- 
tous cells. 
The sclerotized brown membrane, which occurs only in the 
Filicinem, is extraordinarily resistant to acids and other chemical 
agents. Treatment with eau-de-Javelle showed that the colour and 
hardness are not due to lignification, but to the deposition of a foreign 
brown substance in the membrane. The chemical nature of this sub- 
stance appears to be identical with that known as phlobaphene be- 
longing to the group of humin-substances, which has been obtained 
in many instances from bark. The main physiological purpose of 
these layers appears to be to replace the cork which is never found in 
ferns. 
Stem of Ferns.* — M. Leclerc du Sablon contrasts the structure of 
the stem of flowering plants with that of ferns, and then takes special 
instances of the latter, and describes them in detail. In ferns, in place 
of the single central cylinder surrounded by cortex, we have several 
fibrovascular bundles, each with a special endoderm in the middle 
of an irregular cortex. The collateral bundles of Phanerogams are 
then contrasted with the bicollateral or concentric fibrovascular bundles 
of ferns ; and, in the various forms of the latter, the following will 
be found to be common to all. In a developed stem, if nothing has 
been destroyed: — (1) there will be towards the base a conical region, 
the oldest part, and (2) a cylindrical region which elongates indefi- 
nitely. The passage of the root into the stem is always the same. 
The first root incloses two xylem-bundles and two phloem-bundles; 
in passing into the stem, the two xylem-bundles unite by their base, 
and the two phloem-bundles form a complete ring round the xylem. 
Certain species have pith in the centre of the central cylinder, in the 
middle of the xylem, and this is composed of parenchyme ( Polypodium 
aureum , Osmunda regalis). In other cases ( Pteris aquilina , Nephrodium 
molle ), the tissue in the interior of the xylem is formed of phloem- 
elements together with parenchyme. 
Transformation of Roots into Shoots in Ferns-t — From experiments 
made chiefly on Aspleniunn esculentum , Platycerium alcicorne , P. stem - 
maria, P. HUH, and P. Willinkii, Herr S. Rostowzew has determined 
that the root can be transformed directly into a shoot, the apical cell 
of the root becoming the apical cell of the shoot, and being no longer 
segmented in the direction of the root-cap, but only on the three other 
sides. The vascular bundle passes directly into the shoot, and undergoes 
* Ann. Sci. Nat., xi. (1890) pp. 1-15 (2 pis.). 
f Flora, lxxiii. (1890) pp. 155- 68 (1 pi.). 
