ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
551 
support by means of a mucilaginous secretion, which exudes only at early 
contact from the apices of hairs which cover the whole surface of the 
disc. Their sole function appears to be to assist the plant in climbing. 
The discs are developed endogenously immediately above the axils of 
the leaves. Each is made up of a parenchyme with a central plate of 
tracheids, in connection with the bundles of the stem at the base of the 
disc. When growing in a moist atmosphere the discs will sometimes put 
out roots. 
Structure of Halophytes.* * * § — Prof. E. Warming describes the struc- 
tural peculiarities of salt-loving plants from various climates, comparing 
them with xerophytes, between which two classes there is no well- 
marked division-line. Reference is made to 90 species, which are 
arranged under 16 classes. The leaves are usually fleshy and succulent, 
with thick cuticle and depressed stomates. Spongy parenchyme is rare. 
The mechanical tissue is, as a rule, feeble, and the plant is but seldom 
covered with hairs. 
Morphology of Viola. — Herr H. Kramer f has undertaken a careful 
examination of the structure of the various organs of Viola , especially of 
V. tricolor and its allies. Among the more interesting of the results are 
the following : — Many of the epidermal cells, e.g. those which lie between 
the guard-cells of the stomates, are divided by a tangential wall into 
two cells, the outer one of which remains as an epidermal cell, while the 
inner one is connected into a mucilage-cell. The wall of the mucilage- 
cell consists of pure cellulose, and is very frequently provided with 
simple dots. These mucilage-cells appear to occur in all species of 
Viola , and in all the foliar organs except the stamens. 
Prof. V. B. Wittrock t records the results of a similar examination 
of the species belonging to the section Melanium of Viola. The flowers 
differ remarkably, both in size and marking, at different periods of the 
year ; the pollen-grains are also dimorphic or trimorphic. V. tricolor is 
(in Sweden) as a rule cross-pollinated by Lepidoptera and Hymenoptera ; 
while the nearly related V. arvensis is usually self-pollinated ; and there 
are corresponding differences in the two species in the arrangement and 
markings of the parts of the flower. 
The author enters into further details respecting the vegetative 
organs of the species of Viola in question, and then discusses their phy- 
logenetic relationships, and the origin of the various cultivated forms. 
Contractile Roots.§ — Herr A. Rimpach sums up the facts known 
with regard to contractile roots, which he finds in 70 species belonging 
to 20 orders of Monocotyledons and Dicotyledons. They have been 
observed only in herbaceous, and especially in geophilous plants. The 
greatest amount of contraction was to the extent of 70 per cent. In 
Monocotyledons it is only the inner parenchyme of the cortex that takes 
* D. K. Dansk. Vidensk., viii. (1897) pp. 173-272. See Bot. Centralbl., lxxi. 
(1897) p. 455. 
f ‘ Viola tricolor L., in morph., anatom., u. biol. Beziehung,’ Marburg, 1897, 
67 pp. and 5 pis. See Bot. Ztg., Iv. (1897) 2 te Abth., p. 177. 
X Acta Horti Bergiani, ii. (1896, 97) Nos. 1 and 7, 78 and 142 pp., 15 pis. and 
87 figs. See Bot. Centralbl., lxxi. (1897) pp. 133, 140. 
§ Beitr. z. wiss. Bot. (Fiinfstuck), ii. (1897) pp. 1-28 (2 pis.). Cf. this Journal, 
ante, p. 307. 
1897 2 q 
