362 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
parenchymatous or becomes sclerenchymatous. But when, as is the case 
with most Dicotyledons, there is an unbroken cambium ring which 
forms secondary xylem and phloem, the perimedullary zone is developed 
in various ways. It may either remain unlignified, or the inner part 
only, or the outer part only, may be lignified ; or it may consist entirely 
of cellulose ; or it may become completely lignified. In all cases the 
cells of the perimedullary zone are longer than those of the pith. They 
may become the seat of new formations. At the apex of the vascular 
bundle a meristem may be formed that either undergoes no further 
differentiation, or produces bundles of sieve-tubes and vessels. The 
formation of the internal phloem of bicollateral bundles is due to this 
zone. The inner is therefore always a later formation than the outer 
phloem. 
The special development of the perimedullary zone is described in a 
large number of species, woody and herbaceous, belonging to various 
natural orders, mostly dicotyledonous. 
Flexibility of the Stem of Climbing Plants.* — Herr H. Schenk 
discusses the cause of the greater flexibility of the stem of climbing 
shrubs as compared with those which do not twine. The species speci- 
ally examined were Aristolochia tomentosa , Clematis Vitalba , Wistaria 
chinensis, and Periploca grseca. The last shows a normal growth, while 
the other three present the peculiarity of the new formation of successive 
layers of cambium forming xylem and phloem, outside the original 
normal cambium. In the first two species named the xylem is composed 
of detached plates separated by thin-walled parenchyme, the layers of 
cambium and the sieve- bundles being still in close connection at the 
periphery. 
Structure of Thymeleaceae and Peneaceae.f — From an examination 
of the histological characters of a large number of genera and species 
belonging to these two natural orders, M. P. van Tieghem concludes 
that the Thymeleaceae should be placed among the Dialypetalae with 
inferior ovary, near to the Combretaceae, and that the Peneaceae belong 
also to the same group, but show the greatest affinity to the Melasto- 
maceae. The Thymeleaceae are divided into three sub-orders — the 
Drapeteae, Thymeleae, and Aquilarieae. In the genera Ptikleia and Ste- 
phanodaphne (Thymeleae), and Lophostoma (Aquilarieae), the cortical 
cells of the leaf contain remarkable filiform sclerites, which branch in 
all directions, ending beneath the epiderm, mostly between this layer and 
the palisade cells of the upper surface. 
Anatomy of Galegese.J — According to Herr J. Weylandt, the most 
marked characteristic of this tribe of Papilionaceae is that the stomates 
are almost invariably surrounded by several bounding-cells arranged 
irregularly round the guard-cells. Tannin-sacs occur, as in the other 
tribes, containing not only tannin but also albumen. 
Anatomy of Ataccia.§ — M. C. Queva describes the anatomical struc- 
ture of the stem and root of Ataccia cristata (Tacciaceae). The stem 
* Flora, lxxvii. (1893) pp. 313-26 (2 pis.). 
t Ann. Sci. Nat. (Bjt.), xvii. (1893) pp. 185-294 (1 pi.). 
X ‘ Beitr. z. anatom. Ciiarakt. d. Galegeen,’ Miincken, 1893. See B:>t. Contralbl., 
lvi. (1893) p. 39. § Comptes Rendus, cxvii. (1893) pp. 409-12. 
