AFRICAN GRASS FIRES AND THEIR EFFECTS. 79 



dance ; there will be usually 500 of one of these species to 

 every individual of some other kind. I brought home 

 specimens of the bark of these six or seven forms, which 

 were given to Professor Bretland Farmer for examination, 

 who replied as follows : " I examined your specimens of 

 bark and they all agree in possessing cells which show a 

 certain amount of gummy degeneration of the cells in the 

 bark, together with the presence of a considerable amount 

 of sclerotic cells ; it seems not impossible that these two 

 facts may be connected with the resistance of the plants to 

 the fires, and I found as a matter of fact that, on comparing 

 the rate of burning of these barks with that of laburnum, 

 they were very slowly consumed. 



" I should have added that there are repeated periderms, 

 and intermixed with the cork are the sclerotic cells 

 already mentioned." Now the artificially produced cork 

 of commerce shows great similarity in some respects to 

 the cork of these fireproof trees. The process adopted 

 both with the birch and the cork oak is to carefully peel off 

 the cracked superficial layer of bark or " male cork " (this is 

 known as "demasclage"). After this the layer of cork 

 increases enormously and may perhaps attain to 17 cm. 

 in thickness if left untouched : the result is the ordinary 

 commercial article. I do not think that it is going too far 

 to say that we have in grass fires a natural " demasclage " 

 process, for they will certainly destroy the outer more or 

 less dead tissues. 



From the researches of Henslow, 1 Tschirch 2 and 

 Volkens 3 on desert plants, it may be considered proved 

 that cutin, which most modern authorities consider nearly 

 identical with suberin, is directly increased by dry and arid 

 conditions, so that this direct effect is probably also of 

 use in increasing the deposition of corky matter. Both 

 evils — -the fire and the drought — have, as so often happens, 

 brought about their own remedy. The sclerotic cells (or stone 

 cork ?) may doubtfully be set down to the same cause, for 



1 Origin of Plant Structures. 



2 Angewandte Anatomie and Linnea, 1881. 



3 Flora der egypt. arab. IVuste. 



