190 Alfred J. Ewart: 



acid is suffieient at 15 to 20 deg. C. to produce an optimal action 

 on germination. As the temperature rises the action of the acid 

 is more rapid ; at 30 deg. C. it is about twice as active as at 

 20 deg. C. The acid must be concentrated. Slight dilution 

 lessens the action greatly, and renders it more dangerous. 

 During the longer soaking in somewhat diluted acid, the seeds 

 are able to absorb the ajcid as the coats are acted on, whereas 

 the strong acid keeps them dry and unswoUen, and only such 

 surfaces as the acid actually touches are corroded and destroyed. 



Biologic Value of Hard Seeds. — As already mentioned, such 

 seeds distribute themselves in time raither than in space, of each 

 year's crop some being destined to remain germinable in the soil 

 for very many years until the parent plants have been cleared off 

 by fire ur drought. In the case of Callistemon rigida and similar 

 plants the seed is largely retained on the parent plant until fire 

 or drought causes the death of the parent plant and the shedding 

 of the seed, which may only take place when some at least of 

 the seeds are 10 or 20 years old. In Araria, Viminaria 

 denudata, Goodia lotifolia and the like, the s^eed are shed, but 

 lie in the soil. To some extent these macrobiotic seeds are 

 adaptations to bush fires, which were probably of common 

 occurrence long before the advent of civilised or even uncivil- 

 ised 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 huums more or less, not 

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

 which the next rain falling on the warm gi-ound aids in soften- 

 ing 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 addi- 

 tion, slight charring of the surface of the seed makes it per- 

 meable 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 away, and the source of nitrates 

 hence removed. They steadily enrich the soil again, and pro- 

 duce 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, etc., whose seeds have lain 



