ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
765 
cambium, and cortex. They are entirely or partially imbedded in the 
cortical parenchyme, outside the primary hard-bast-bundle of the stem, 
though they frequently project into the soft-bast. They may arise 
either in connection with a bud or not ; in the latter case there are two 
principal types, — tubers with a central woody tissue, and those which 
have a corky structure in their centre. 
Leaves of Xerophilous Liliifloreae.* — Herr C. Schmidt has examined 
the structure of tbe leaves in a number of species belonging to the 
orders Xerotideae and Haemodoraceae, natives of arid climates or situa- 
tions. The epiderm is nearly alike on both sides of the leaf ; its cells 
have a thin but distinct cuticle, and are adapted for the storing up of 
water ; trichomic structures are very rare. The mechanical system is 
strongly developed, and is composed of typical bast-cells with greatly 
thickened walls. The assimilating system consists of typical palisade- 
cells ; there is never a well-developed spongy parenchyme. The aerating 
system is well developed, but consists only of narrow crevices. The 
stomates always have their longer axis parallel to the axis of the leaf ; 
they are alike in number and form on the two sides of the leaf ; the 
thickening-bands in the guard-cells are remarkably strongly developed, 
leaving only a very narrow interval between them. Tbe conducting 
elements are nearly always in close contact with the assimilating system. 
Dispersed through the fundamental tissue are frequently very elongated 
cells destitute of chlorophyll and containing bundles of raphides. 
Abnormal Leaves.f — Herr J. Klein has attempted to trace the laws 
which govern the appearance of abnormalities in leaves, especially in 
relation to coalescent or double leaves. He finds that when leaves bear 
on one petiole two more or less separated laminae, each with its own 
mid-rib, — if this is the result of the union of two leaves, there are 
always a larger number, usually double as many, vascular bundles in 
the petiole as in that of an ordinary leaf ; if tbe result of division, only 
tbe ordinary number of bundles. A double leaf results from the 
coalescence of two rudiments of leaves, a divided leaf from only one. 
Roots without a Root-cap.J — Herr T. Waage has made an exami- 
nation of the exceptional cases in which a true root is not provided with 
a root-cap, especially in the Hippocastanaceae and Sapindaceae. He finds 
all intermediate stages between these and the normal structure of a root 
provided with a root-cap. The purpose of the capless roots appears to 
be to assist in the increased absorption and storing up of water where 
this is required. The various degrees of non-development of the root- 
cap may be summed up as follows : — The cap may be greatly reduced ; 
and either with unlimited growth, as in Trapa natans, or with temporarily 
limited growth, as in Sapindus Saponaria, and partially in other 
Sapindaceae. The root may have at first a true cap, which may become 
changed into a permanent root-cap as in the Lemnaceae, or may be 
completely thrown off, as in Azolla, Hydrocharis, Pistia, and in the 
Bromeliaceae. The root may be from the first destitute of a cap ; and 
then the growth may either be limited for a time, as in Ungnadia , 
* Bot. Centralbl., xlvii. (1891) pp. 1-6, 33-42, 97-107, 164-70 (1 pi.). 
f Ungar. Acad. Wiss., June 15, 1891. See But. Centralbl., xlvii. (1891) p. 262. 
X Ber. Deutsck. Bot. Gesell., ix. (1891) pp. 132-62 (2 pis.). 
