ZOOLOGY AND BOTANY, MICROSCOPY. ETC. 
45 
the other hand (in bulbs of Allium cepa and seeds of Pisum sativum ), 
a substance identical in chemical composition with animal haematogen. 
The same substance was found also in Mucor mucedo , Boletus edulis, and 
Bacterium megaterium. Its function appears to be to take part in the 
formation of the cell-nucleus in young organs ; and the author believes 
iron to be, like phosphorus, an essential constituent of the nucleus. 
(3) Structure of Tissues. 
Histology of the Growing Point.* — Herr A. C. Hof has followed 
out the karyokinetic processes and the origin of vacuoles in the growing 
point, and the nature of the apical cell, in Pteridophyta, Gymnosperms 
(Ephedra), and Angiosperms ( Vicia ). The vegetative cone is sur- 
rounded by a well developed “ calyptra,” composed of superposed caps 
(in Pteris of only a single layer). The apical cell and the adjacent 
segments are distinguished by the small amount of cell-contents ; the 
apical region is characterised by an abundance of vacuoles. The author 
confirms De Vries’s statement of the origin of the vacuoles from others 
previously in existence ; in other words, as Strasburger says, from the 
honeycomb-structure of the alveolarplasm ; they are in no sense special 
organs of the protoplasm. 
The karyokinetic processes are described in detail in the apex of 
the root of Ephedra major and Vicia Faba. The nuclear threads do 
not consist of alternate discs of linin and chromatin, but of an uninter- 
rupted filament of linin in which discs of chromatin are imbedded. 
The chromosomes have mostly a J-form. "During metakinesis they 
become arranged into a diaster. The daughter-knot-stages are derived 
on both sides from the chromosomes of the diaster, and this process 
ends in the formation of the two daughter-nuclei with a reticulate 
chromatin-framework. Finally, the author is of opinion that the multi- 
polar and bipolar origins of the nuclear spindle are not essentially 
distinct, but are connected by intermediate processes. 
Healing-Tissue in Plants. j — M. J. Massart treats in detail of the 
various modes in which wounds are healed in plants. 
In Algae with free filaments, two modes are exhibited : — -A lateral 
outgrowth of the nearest cell below, and a proliferation of the injured 
cell by the upper and under adjacent cells. In Algae which form plates 
of cells, the row whose terminal cell is injured ceases to grow, and the 
adjoining cells fill up the vacancy. In Algae with a more complicated 
thallus, it is only the parts destroyed that are regenerated, whether 
growing points or older elements. Among Fungi some are able to 
regenerate the lost portions, while others have not this capacity. 
Heteromerous Lichens form a new cortical layer. 
Muscineae and Pteridophyta show, in general, but little power of 
recovery from injuries; the Marattiaceae replace the lost tissues by 
cell-division, but there is no formation of cork. 
Among Phanerogams there are two chief processes which take place 
in the adjacent tissues : — an elongation of the meristematic cells towards 
the wound, together with the formation of numerous walls parallel to 
* Bot. Centralbl., lxxvi. (1898) pp. 65-9, 113-8, 166-71, 221-6 (2 pis.). 
t ‘ La Cicatrisation chez les vege'taux ’ : Mem. couronnes Acad. r. de Belgique, 
1898, 68 pp., 57 figs. 
