1 1 Nov., 1912.] 



On Wattles and Wattle-Bark. 



689 



Acacia Merralli 



„ montana 



„ vujrtifolia 



„ neriifolia 



,, nervosa 



„ Oswaldi 



,, pcnninervis 



„ pentadenia 



., Senegal 



;, Simsii . 



., suaveolens 

 verniciflua 



In each sample of air-dried seeds it is the hard seeds whicli last 

 longest, and in the soil it is only these hard, non-swelling seeds which 

 •can last for any length of time. In my paper on the "Longevity of 

 Seeds," I have used the term "macrobiotic" to denote seeds of this 

 ■character which are specially adapted for dispersal in time rather than 

 in space.* 



To some extent these macrobiotic seeds are adaptations to l)iish 

 fires, which were probably of common occurrence long before the advent 

 of civilized or even uncivilized man, and must have been far more 

 frequent than at present when the lava was flowing from the volcanoes 

 <of Victoria. 



Such bush fires, after burning off the humus more or less, not only 

 partly expose the seeds, but leave behind an alkaline ash, which the 

 next rain falling on the warm ground aids in softening the coats of 

 the hard seeds, and bringing about their germination. When the ash 

 is abundant and very alkaline the seedlings may be killed, but some 

 will always survive. In addition, slight charring of the surface of 

 the seed makes it permeable to water without necessarily destroying 

 the vitality of the contents. The acacias or other leguminous plants, 

 by the aid of their root-nodules, can grow in soil from which all, or 

 nearly all, the humus has been burnt aw^ay, and the source of nitrates 

 hence removed. They steadily enrich the soil again, and produce the 

 conditions for the growth of large forest trees. These, if destroyed 

 by a devastating bush fire, may once more be replaced by the humus- 

 forming acacias, &c., whose seeds have lain dormant in the soil during 

 part, at least, of the growth of the forest. 



I have, in fact, found acacia seeds deeply buried in the soil of 

 gum forests, where no other signs of their presence could be seen, 

 and where no other acacias were present within at least a mile. In 

 iiddition, the following data on page 690 may be given of the number 

 of germinable acacia seeds per 2-in. cube of soil found at various 

 ■depths mider old acacias growing in undisturbed primeval bush. 



A square pole of such soil would in the top 18 inches, in some cases, 

 contain sufficient germinable seed to stock several square miles of 

 territory, so that the amount of margin allowed for accident is very 

 great, and even a very low percentage germination would suffice to 

 re-cover the soil with the original vegetation after the severest bush 



» See " Longevity of Seeds" in Proc. Roy. Soc. Vict., 21 (N.S.) Pt. 1 1908. 



