470 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Herr 0. G. Petersen has come to the conclusion that the ordinary con- 
ception that the increase is effected by means of a special meristem 
only in the case of the arborescent Liliacese is incorrect. There is, 
on the contrary, a gradual passage from the type of Dracaena to that of 
the Orchideae, where there is a complete absence of meristem. This 
latter is the case in the stem of Vanilla Pompona and Vanda tricolor , in 
the green aerial tubers of species of Epidendron , and in the thick rhizome 
of Typha. From an anatomical point of view the author distinguishes, 
in the stem of Monocotyledons, the cortex and the central cylinder, the 
latter being again composed of the pericycle (when present), the bundle- 
layer, and the pith. 
Palisade-cells and Transpiration.* — M. P. Lesage adduces argu- 
ments in favour of the view that the palisade-tissue of leaves is an 
apparatus for protecting the plant from excessive transpiration. These 
are derived from the following facts : — Palisade-cells attain a fuller 
development in the light than in the shade, and in dry than in moist air. 
In submerged leaves they are entirely wanting. In Alpine plants, and 
in plants growing in a salt soil, the palisade-tissue is especially strongly 
developed. 
Medullary Rays of Dicotyledonous Herbs and Shrubs. f — Herr A. 
Herbst has made a study of the structure of the medullary rays in 
herbaceous and shrubby plants belonging to a great number of different 
natural orders of Dicotyledons. Several points are, he says, of consider- 
able use for purposes of classification, especially the number of rows of 
cells of which the rays are composed. Although the thickening of the 
wall of these cells is usually only slight, yet there are considerable 
variations in this respect. The medullary rays consist either of so-called 
“ palisade-cells ” only, or of “ mesenchyme-cells ” only, or of both kinds , 
but this character can be used only in the determination of species. 
Both in the summer and in the late autumn there is in the medullary 
rays an abundant intercellular system. This may often run through 
the whole of the ray and through the cambium as far as the bark, and 
communicate with the external air through stomates or lenticels. 
The author confirms the hypothesis of Russow, that the bordered pits 
of the medullary rays serve for the conveyance not only of water, but 
also of air. The imperfectly bordered pits on the sides of the cells 
which face intercellular spaces appear to indicate that the latter are of 
schizogenous origin. 
Witch-broom of the Fir. J — M. E. Mer describes in detail the 
structure of the excrescence ( chaudron ) from which grows the tuft of 
fascicled branches known as “ witch-broom,” caused by the attacks of 
a parasitic fungus, JEcidium elatinum. While the cortex and liber of the 
trunk acquire a hypertrophied development, those of the vascular bundles 
are partially suppressed. The cambium, which is at first excited to an 
increased activity, finally perishes. The ultimate result is always the 
death of the tree. 
* Comptes Rendus, cxviii. (1894) pp. 255-8. 
t Bot. Centralbl., lvii. (1894) pp. 257-66, 289-98,321-30, 353-61, 401-13 (1 pi.). 
Rev. Gen. de Bot. (Bonnier), vi. (1894) pp. 153-73. 
