ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
895 
character.* They spring either from the upper or from the under side 
of the leafy shoots, and at once direct their growth downwards. They 
are occasionally themselves transformed into leafy shoots. When they 
reach the soil, roots of ordinary structure force themselves through the 
swollen apex of the aerial roots, the outermost cells of the latter becoming 
converted into mucilage. This appears to be the result entirely of the 
absorption of water and not simply of contact. All the roots branch 
in a monopodial and not in a dichotomous manner. The branching of 
the roots in the soil appeal's to be in the first place the result of the 
moisture of the soil ; the nutrient substances contained in it determining 
their further development. 
Biology of Ferns. f — Prof. V. B. Wittrock has investigated several 
points in the biology of Ferns. He finds that complete desiccation of the 
frond for a considerable time in a sulphuric acid chamber does not (in 
Polypodium vulgare) inflict the least injury on the plant. The frond is 
able to absorb water in large quantities from the atmosphere directly 
through its surface. In many native species (of Sweden) such a desicca- 
tion takes place regularly in the winter ; each species has its own 
special “ dry position ” of the leaves. In Polypodium vulgare the fi'onds 
assume a special “ cold position ” at the commencement of winter, con- 
sisting in the turgid segments of the fronds curving upwards, so that 
the frond takes the form of a cylinder. In many species of Polypodiaceae 
the frond begins to die off from below, the apical portion remaining 
living and turgid, while it continues to absorb moisture directly from 
the air. In many species the bursting of the sporanges and dissemina- 
tion of the spores takes place naturally in the winter or very early 
spring. In some species fronds which have lain for a long period 
in the herbarium can be restored to a turgid condition, in one case as 
much as 22J months ; while Selaginella lepidophylla showed signs of 
life after having been more than 11 years under a bell-glass, the water 
being absorbed through the stem and surface of the leaves. Revived 
herbarium specimens of ferns may put out new fronds and roots. 
Ophioglossum.f — M. S. Rostowzevv has undertaken a careful exami- 
nation of the structure and development of the vegetative organs in 
Ophioglossum vulgatum. In the bud-condition the single leaf of each 
year is almost entirely concealed by a sheath, and the orifice of the 
canal which traverses the bud is not situated at the summit of the sheath, 
but on its ventral side on a triangular prominence. The summit of the 
stem is cup-shaped, and the growing point is situated at the base of the 
cavity. The development of the leaf is very slow ; its fertile portion or 
spike takes three years for its complete development. The initial cells 
of the sporanges are indistinguishable from the neighbouring meriste- 
matic cells. They divide into two, of which the interior is the arehe- 
spore, while the exterior produces the wall of the sporange ; this is 
ultimately composed of three layers of cells. The outermost layers of 
cells derived from the archespore are barren, and constitute an epithele 
or tapete. The prothallium and embryo (sexual generation) of 0. vul- 
gatum are at present entirely unknown. 
* Cf. this Journal, 1891, p. 765. 
t Acta Horti Bergiani, i. 58 pp. See Bot. Centralbl., xlix. (1892) p. 132. 
t Overs. K. Dansk. Yidensk. Sclsk. Forhuudl., 1891, pp. 51-82 (2 pis. and 17 figs.). 
