ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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rapidly and become spherical, while atrophied grains remain small and 
elliptical, or irregular in form. In the group Sijnstylse the pollen was 
found to be abundant and perfect, while in the Caninw, B. canina for 
example, the proportion of well-developed grains varied from one-third 
to two-thirds. In the groups Carolinw, Cinnamomese, Pimjpinellifolise, 
and Sericese, the pollen was generally found to be abundant and perfect. 
Variations of Water in the Perianth."^ — M. Emery gives the results 
of various experiments made to ascertain the amount of water in the 
perianth. The law of variations of the amount of water presents two 
cases for terrestrial plants, according as they grow under normal con- 
ditions or in a medium saturated with moisture. In the first case, the 
point of maximum imbibition corresponds with a middle phase of the 
life of the perianth ; in the second case, the maximum point and relative 
weight of water increases without ceasing from the commencement of 
flowering to the fall of the perianth. 
Extrafloral Nectaries.j — Herr E. Ludwig describes the structure of 
the extrafloral nectaries in a number of myrmecophilous plants, and the 
mode in which the ants are attracted to them. In Impatiens halsaminea 
they consist of a number of hairs containing a red pigment, closely 
adpressed to the stem and with their apex pointing upwards; while 
those which are intended as a protection against creeping insects have 
their apex pointing downwards. In J. cristata and tricornis the road to 
the dark-red extrafloral nectaries is indicated by a row of red dots, 
which, like the nectaries themselves, are serrations of the leaf, and 
sometimes also themselves develope a secretion. Even the young 
seedling is protected in this way from the attacks of ants. In Sambucus 
racemosa, Viburnum Opulus, and other plants, the nectaries themselves, 
attached to the leaf-stalks, are rendered conspicuous by a very bright 
colouring. 
Tearing of the Leaves of Musacese.J — Herr C. Lippitsch describes 
the mechanical principle on which this phenomenon, characteristic of all 
the families of the Scitaminefe, viz. the Musacem, Cannacem, Marantaceas, 
and Zingiberaceae, depends. He points out that this tearing inflicts no 
injury on the assimilating functions of the leaf, and that the plant is 
thereby spared any unnecessary consumption of energy in the production 
of strengthening tissue. The margin of the leaf is provided with small 
narrow wings, which serve, when young, as a reservoir for water. In 
older leaves these wings dry up, and it is the contraction connected 
with this desiccation which causes the rupture of the tissue of the leaf. 
Leaves and Shoots of Euphorbiacese and Cactaceae.§ — Herr X. 
Wetter wald describes in detail the structure and development of the 
stem and leaves in the succulent species of Euphorbia^ of which nineteen 
are named, and in several genera of Cactacese, viz. Opuntia, Peireskia, 
Phyllocactus, Epiphjllum^ Cereus, Echinopsis, Pilocereus, Ecliinocactus, 
Echinocereus, and Mammillaria. In both groups there are forms with 
* Bull. Soc. Bot. France, xxxvi. (1889) pp. 322-33. 
t Humboldt, viii. (1889) pp. 294-7 (4 figs.). See Bot. Centralbl., xl. (18S9) 
p. 79. Cf. this Journal, 1889, p. 543. 
X Oesterr. Bot. Zeitschr., xxxix. (1889) pp. 206-10, 259-63 (I fig.). 
§ Nova Acta Acad. Cses, Leop.-Carol., liii. (1889) pp. 377-440 (5 pis.). 
