614 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
sembling that of the stem ; or by the formation of a sclero-suberous 
layer beneath the periderm. The only difference between leaves which 
wither on the tree and those which fall before withering, is the incom- 
plete formation in the former case of the separating layer. 
At the zone of the articulation of the petiole, the stereome of the 
vascular bundles is always wanting, the only lignified elements being 
the vessels. The xylem-fibres are wanting, and in most cases also the 
phloem-fibres. Cicatrisation is effected by a sclero-suberous modifica- 
tion of the existing cells similar to that of the fundamental tissue. 
The sieve-tubes are usually destroyed ; the vessels are stopped by the 
production of a gum, or by thyllae, most often by both. 
The crystalliferous cells are never again septated ; their walls under- 
go a sclero-suberous modification. The other isolated secreting cells 
undergo no change in the cushion. The branched laticiferous cells 
close up, before the fall of the leaf, by two septa, one above the 
separating layer in the petiole, the other below it, in the cushion. 
Fall of the Leaves of Monocotyledons.* — M. E. Fouilloy finds 
that in certain genera of Orchideae belonging to Tropical America — 
Octomeria , Bulb ophy llum — with thick deciduous leaves, the region of the 
leaf where its detachment is effected becomes differentiated at an early 
period. Long before the period of the fall of the leaf, it is readily 
distinguished from the tissues which bound it as a layer still composed 
of very small cells which retain their cellulose character. 
Anatomy of the Root and Stem of Chenopodiacese.f — M. G. Fron 
has studied the structure of the axial organs in various genera of 
Chenopodiaceae. In the root he finds two modes of arrangement of the 
vascular bundles, symmetrical and asymmetrical ; the latter resulting 
from an unequal development of the two primitive phloem-masses. 
This difference is correlated with a difference in the structure of the 
embryo. When, in the embryo, the radicle is not in contact with the 
cotyledons, the final structure of the root is symmetrical ; when the 
radicle is in close contact with the cotyledons, the root is asymmetrical. 
The spiral arrangement of the vascular bundles cannot be taken as a 
generic character. The secondary formations are produced by a dif- 
ferent mechanism in the root and in the stem of the same species. In 
the stem the course of the vascular bundles is sometimes straight, 
sometimes wavy. The passage from the root to the stem structure 
takes place at very different points in the hypocotyledonary axis. 
Gall of Aulax Papaveris.f — M. M. Molliard describes the deforma- 
tions produced in the capsule of Papaver Bhceas and dubium by the 
larvae of Aulax papaveris. In the centre of the capsule is a mass of 
white cellular tissue, containing well-defined cavities in which are 
found the larvae. The placentae are greatly hypertrophied. The hyper- 
trophied tissue subsequently becomes differentiated into a nutrient tissue 
for the parasite, a sclerenchymatous ring, and a parenchyme. The 
ovules are completely atrophied. The peduncle of the diseased capsule 
is very liable to be attacked by Peronospora arbor escens. 
* Rev. Gen. de Bot. (Bonnier), xi. (1899) pp. 804-9 (6 figs.). 
t Ann. Sci. Nat. (Bot.), ix. (1899) pp. 157-240 (6 pis. and 22 figs.). 
% Rev. Gen. de Bot. (Bonnier), xi. (1899), pp. 209-17 (11 figs.). 
