ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
51 
Reaction of Leaves to continuous Rainfall.* — From a series of 
experiments made by Prof. D. T. MacDougal on tbe influence of a 
continuous rainfall upon leaves, be concludes that a direct effect on the 
structure of the leaf is produced, but that the nature of this change 
differs in different species. In addition to the hitherto recognised 
characters of adaptation to a heavy rainfall, the author adds an upwardly 
convex form of the lamina of the leaf. 
Petiole of Qnercus.f — M. F. Bosseboeuf distinguishes two distinct 
types in the petiole of different species of oak (1) At the base of the 
petiole the numerous isolated vascular bundles are arranged in a circular 
line, flattened above, or nearly triangular ; at the back of each of the 
bundles is a mass of sclerenchyme proceeding from the pericycle, with 
very strongly thickened walls. (2) The vascular bundles, also isolated 
at the base, but less numerous, soon unite to form a complete ring, 
flattened above, composed of a layer of internal xylem and one of 
phloem, and surrounded by the strongly thickened pericycle; this 
arrangement continues through the rest of the petiole and the median 
vein of the lamina ; there is never any internal arc. Varieties of each 
type are described ; and there are also intermediate forms, 
0 . Physiology. 
CP Reproduction and Embryology. 
Embryology of Balanophoracese.J — M. P. van Tieghem describes 
the structure of the male and female flowers in the different genera of 
this order. They may be classified under three families, characterised by 
the structure of the ovary in the female flower. In the first (Sarcophy- 
tideae) there are as many rudimentary and transitory ovules as there are 
earpels ; they are orthotropous, pendant, and basigamous, and the ovary 
is plurilocular, with axile placentation. In the second (Helosidese) there 
are no ovules, but only a placenta, enclosing as many endosperm mother- 
eells as there are carpels ; they are acrogamous, and the ovary is unilo- 
cular, with central placentation. In the third (Balanophorideae) there are 
neither ovules nor placenta ; but the monocarpellary ovary produces, 
beneath the epiderm of its base, a single acrogamous endosperm mother- 
cell. The order must be placed in the sub-class of Dicotyledons 
destitute of ovules, i.e. in the Loranthinese. 
Embryo-Sac of Succulent Plants.§ — A detailed study of the repro- 
ductive organs of succulent plants— especially the Cactacem, Mesem- 
bryanthemaceae, and Crassulaceae — leads M. E. d’Hubert to the conclusion 
that there are several features characteristic of this class of plants, 
though not absolutely confined to it. 
In the Cactaceae the ovules are so arranged as to fill up as completely 
as possible the cavity of the ovary ; they are amphitropous and bitegu- 
mented. The funicle is always strongly developed ; it is coiled round 
it, forming a complete envelope (the aril of Opuntia), and is loaded with 
starch ; it serves both to protect and to nourish the ovule. The embryo- 
sac is formed only at a late period, the axile hypodermal cell of the 
* Bot. Gazette, xxii. (1896) pp. 232-3. 
f Bull. Soc. Bot. France, xliii. (1896) pp. 260-6 (8 fio-s.Y 
% Tom. cit., pp. 295-310. 
§ Ann. Sci. Nat. (Bot.), ii. (1896) pp. 37-128 (3 pis. and 61 figs.). 
