478 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
number. Generally the pericyclic fibres become less numerous at the 
nodes ; at the same time their walls are thinner and their size increases. 
These modifications are especially noticeable in the neighbourhood of 
emergent bundles ; but it is in the xylem of the fibrovascular bundles 
that the greatest change takes place. The vessels diminish in diameter 
and become more numerous; the medullary rays also become more 
numerous and larger. The pith also increases, but in a smaller ratio 
than the cortex. 
Sap-periderm.* — By this term Herr J. Wiesner designates a tissue 
found in aerial, but more often on underground parts of plants. It is 
distinguished from ordinary periderm by both its cell-wall and its 
contents being in a living condition, serving as an absorption-tissue for 
the storing up of water. It is always the tissue from which the ordinary 
periderm is formed. In the tuber of the potato it occurs as a stratum, 
often from six to ten cells in thickness, between the dead periderm and the 
phellogen, already passed into a permanent condition, cell-division having 
ceased in it ; but the cells contain remains of protoplasm, and frequently 
a nucleus. As long as the potato remains in the soil this sap-periderm 
only is formed ; the dead periderm, the cells of which are empty, is 
produced subsequently as a result of desiccation. This tissue occurs 
also in young twigs of the maple and lime, and may persist through 
the winter, but soon becomes covered by ordinary dead periderm. 
Change of Shape exhibited by turgescent pith in water.f — Miss 
Anna Bateson calls attention to the fact that when turgescent pith is 
placed in water it increases greatly in length, but we have no accurate 
knowledge of any changes occurring in the transverse dimensions. The 
general results of a series of experiments directed to this question fall 
into two classes : — (1) The case of the sunflower, elder, and rhubarb, in 
which transverse contraction of the pith is the final result ; (2) Impatiens 
Sultani, in which no contraction occurs ; transverse extensibility is here 
so great that transverse expansion is not only clearly apparent from the 
first, but is never overcome by longitudinal expansion, the pith continues 
to expand transversely, and never exhibits a subsequent contraction. 
Passage from Stem to Boot.J — M. P. A. Dangeard has studied the 
phenomena presented by the tissue at the point of passage from stem 
to root in Dicotyledons. He finds a constant relationship between 
the type of venation in the cotyledons and the number of vascular 
bundles in the root — pinnati-veined cotyledons are associated with a 
root of the diarch type, palminerved cotyledons with a root of the 
tetrarch type. The phloem-bundles behave in the same way as the 
xylem-bundles, but their fusion does not necessarily take place at the 
same level. The term “ collar ” should be reserved for the spot where 
the epiderm of the tigellum unites with the outer piliferous layer of the 
root. It is almost impossible to determine the exact level at which 
the union of the tissues of the two organs takes place. The author 
asserts that the pericycle of the stem is of a different nature from that 
of the root, belonging, in the former, not to the conjunctive tissue, 
* Oesterr. Bot. Zeitschr., xl. (1890) pp. 107-11. 
t Ann. of Bot., iv. (1889) pp. 117-25. 
X Le Botanistc, i. (1889) pp. 75-123 (2 pis.). 
