ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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whether foliar or floral, follow the modifications in the form, whether 
external or internal, and adapt themselves, to a certain extent, to the 
functions which they have to perform. In the stamens they are not 
unfrequently entirely suppressed. In the floral vascular bundles the 
phloem is always differentiated before the xylem. The procambial dif- 
ferentiation advances, in each bundle, from above downwards, and each 
bundle has an independent origin. The fibrovascular system of the 
primary stem is probably formed by the coalescence of the descending 
traces of foliar systems. The floral organs exhibit various modifica- 
tions in the branching and anastomosing, and in the form of the 
bundles, in correlation with the transformations of tho parenchyme 
which they contain. 
Growth of Tracheal Elements.* * * § — Herr A. Nathansohn confirms the 
statement of previous observers that, even in young and growing organs, 
the living protoplasm disappears from the tracheal elements soon after 
their complete development, and simultaneously with the lignification 
of their membrane. As the vessels, whether annular or spiral, still 
continue to increase, this must result in the separation of the rings in 
the former, and the greater inclination of the spiral in the latter case. 
In some cases, at all events, pitted vessels are formed only when growth 
in length has ceased. 
Bursting of the Mechanical Ring in Climbing Plants, f — From the 
examination of a number of trees and shrubs belonging to different 
natural orders, Herr E. Schwabach states that a perfectly closed stereome- 
ring in the young stem occurs only in climbing plants. As the girth 
increases, this mechanical ring bursts, and at the same time the adjacent 
parenchyme cells rich in protoplasm force themselves, by their turgor, 
into the vacancies and distend them. This takes place so quickly that 
it is impossible to find such a cavity which is not filled up by meri- 
stematic tissue. The meristematic cells thus introduced thicken their 
walls and become transformed into stone-cells with extraordinary 
rapidity, and thus increase the mechanical function of the ring. The 
bursting usually takes place in the radial prolongations of the medullary 
rays, especially where the stereome-ring offers the least resistance. 
The penetration of the parenchymatous cells which adjoin the stereome- 
ring takes place on both the outer and inner sides of the ring. 
Pneumathodes and Aerenchyme.f — Herr A. Wieler doubts whether 
the so-called pneumathodes — e.g. those described by Jost in the roots of 
palms — are really organs of aeration. They appear to result from a 
stimulus exercised — in the case of roots — by the water on special groups 
of tissue, by which the epiderm is ruptured, and the injury healed by 
stoppage of the intercellular spaces. The formation of pneumathodes 
on the erect roots of palms may be explained by a conduction of the 
irritation from the submerged to the exposed area. 
Raphid-Cells.§ — Herr P. C. A. Fuchs has investigated the structure 
of raphid-cells, especially with the view of determining tho question 
* Jahrb. f. wi?s. Bot., xxxii. (1898) pp. 671-86 (1 pi.). 
f Bot. Centralbl., lxxvi. (1898) pp. 353-61 (1 pi.). 
% Jahrb f. wiss. Bot., xxxii. (1898) pp. 503-24 (1 pi.). 
§ Oesterr. Bot. Zeitsehr., xlviii. (1898) pp. 324-32 (1 pi.). 
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