736 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
In some trees the primary or superficial periderm persists through 
its whole life, in which case the phellema is continually renewed from 
the phellogen, in proportion as the outer layers peel off. The mistletoe 
is the only woody Phanerogam in which the formation of periderm is 
entirely suppressed. 
The author then proceeds to describe the structure and development 
of the periderm and of the bark in a large number of species belonging 
to the Dicotyledones, Gymnosperms, and Monocotyledones, especially 
comparing the structure of this tissue in the stem and in the root. In 
no case was there found any fundamental difference in this respect in the 
two regions, and in many cases a complete agreement in every particular. 
Where slight differences are manifested, they are obviously related to 
the different environment of the root, and to its smaller increase in 
thickness ; and these consist mainly in the greater regularity and 
simplicity of the phellema in the root as compared to that of the stem. 
The Araucarieae are distinguished from the other tribes of Coniferae 
by the remarkable size of the cells of the periderm. All the species 
examined of the Abietineae were marked by the greater or less develop- 
ment of phelloid. tissue, with thickened and lignified walls, alternating 
regularly with layers of thin- walled suber. In the Taxodineae, the 
CupressineaB, and in many species of Podocarpeae, we find an annular 
bark, and the phelloid tissue is wanting ; the suberous cells are large, 
cubical, uncoloured, and with thin walls. Gingko ( Salisburia ), alone 
among Conifers, has an abundant phellema composed exclusively of 
large suberous elements. 
Development of the Stem of Conifers.* — M. H. Douliot calls atten- 
tion to the two theories on the mode of growth and structure of the 
summit of the stem in Conifers. Hanstein distinguishes at the summit 
of the stem three groups of cells, the dermatogen, the periblem, and the 
plerome, while the conclusions of Nageli are diametrically opposed to 
this. The author then takes several examples, and carefully describes 
their structure. In Picea excelsa the development can be clearly traced, 
and there can be no doubt that the epiderm and the cortex have a 
common origin ; the initial cell is in this case tetrahedral. In Torreya 
nucifera there is a certain amount of analogy with the Equisetaceae, and 
some observers state they can trace three distinct histogenic regions in 
Sequoia semper virens . This, however, is an error. 
Cortical Fibrovascular Bundles.! — Prof. M. M. Hartog describes the 
occurrence, in Gustavia and Lecythis (Lecythideae), of a complete system 
of cortical bundles external to the pericycle, anastomosing with the leaf- 
traces of the central cylinder at the nodes. They have often a complete 
circle of exogenous wood, and are all but concentric. In Stravadium 
racemosum (Barringtonieae) there are similar bundles, but the orientation 
of the liber is reversed. 
Vascular Bundles of Dahlia. J — Dr. O. Ivruch finds the stem of 
Dahlia imperialis to agree with that of many other species of Cichoriacere 
in the presence of medullary vascular bundles, but presents specialities, 
* Journ. de Bot. (Morot), iv. (1890) pp. 206-12 (4 figs.), 
t Ann. of Bot., iv. (1890) pp. 299-300. 
j Nuov. Giorn. Bot. Ital., xxii. (1890) pp. 410-3. 
