586 REPORT—1905. 
Shattock has shown how these cells, when injured by a sharp scalpel, are destroyed, 
and in the healed tissue are replaced by others derived from the division of adja- 
cent cells. 
Richards demonstrated the rise of temperature, and also the increased respira- 
tory activity of wounded parenchymatous cells. 
Nemec has traced the protoplasmic changes in cells adjacent to a wound. 
In the case of parenchymatous tissues little attention has been paid to the 
manner in which the intercellular spaces are closed. Thus, for example, when a 
hyacinth or other leaf is cut, the rate of exchange between the intercellular and 
atmospheric gases is profoundly altered, and the first step towards healing such a 
wound is to seal the openings of the intercellular spaces and restore the rate of 
gaseous exchange to the normal condition. This sealing is accomplished by the 
formation of a substance probably derived from the cellulose wall; it is found 
fully developed in about twenty-four hours from the time of injury, and thus a 
cicatrix is made, which completely prevents the loss of aqueous vapour and of the 
entrance or escape of gases at the wounded surface. This substance is probably 
identical with wound-gum; it reacts to phloroglucin and other stains for lignin, 
and like it is not developed in an atmosphere deprived of free oxygen, such as in CO,. 
The formation of wound-gum may thus in some way be connected with the rise of 
temperature discovered by Richards. 
In addition to the hyacinth leaf, very beautiful preparations of wound-gum— 
showing the characteristic red of the lignin reaction with phloroglucin—can be 
observed in the leaf of Agapanthus, the epicotyl of Avena, the cortex of young 
woody stems, and in the reservoirs of reserve material, such as the swede or turnip. 
In fact, wound-gum appears to be generally developed as a consequence of 
mechanical injury. 
The first step, then, towards the healing of both woody and parenchymatous 
tissue is the closing of the intercellular spaces by a cicatrix prior to the develop- 
ment of bark. 
4, Joint Discussion with Section L on Educational Methods in the 
Teachung of Botany. Opened by Harotp Wacker, F.R.S. 
THURSDAY, AUGUST 17. 
The following Papers were read :— 
1. On the Vegetation and the Floral Elements of Tropical Africa. . 
By Professor A. ENGLER. 
Professor Engler gave first a brief account of the meteorological conditions in 
Africa, especially of the differences of rainfall in East, West, and Central Africa, 
and then enumerated the ‘ formations of vegetation,’ which are especially dependent 
upon the water and the temperature which they receive in the various seasons of 
the year, and also upon the chemical and physical conditions of the soil. One can 
distinguish almost the same formations in every large continental tropical country 
which ascends from the sea to high mountains, although the floral elements, or the 
components of the flora, are more or less different in tropical Africa, in tropical 
Asia, and in tropical America, 
One can first separate the halophilous littoral formations from the others, 
because many littoral plants of East Africa are the same as those of East India, 
and because many of West Africa are the same as those of tropical America. 
Then we have the hydrophilous formations, those which are especially favoured 
by moving or stagnant water, either the whole year, or only for some months or 
weeks, One finds a great variety of hydrophilous formations, and they are very 
luxuriant in those parts of Africa where there is much rainfall, and where water 
does not only come to the roots, but also from the clouds to the leaves, Those are 
7. 
