lo Dec, 1910.] The Nature and Uses of Hard Seeds. 771 



As might be expected, the plant reaps certain benefits by forming 

 seeds of this kind, the chief being as regards the advantageous distribution 

 of its offspring. There are two great methods of distribution, one of 

 which may be termed distribution in space and, to accomplish this, the 

 plants provide the seed with various mechanisms such as spines, tufts of 

 hair, &c., by means of which they are carried from place to place by 

 such agencies as wind, water or animals. In this way the danger of over- 

 crowding is avoided to a great extent. In the second method, — distribution 

 in time — the structure of the seeds is such that they germinate after vary- 

 ing periods, and by this method, the seeds of one year may provide 

 seedlings for many successive seasons. Plants which have adopted this 

 method of distribution produce hard seeds freely. All the soft seed will 

 germinate the first season and the hard ones will remain dormant in the 

 soil. Gradually, the impermeable covering will be removed by various 

 agencies, the least resistant seeds will germinate first, the harder ones 

 remaining for longer period until perhaps the parent plant has been re- 

 moved as the result of drought, bush fires or some other cause. 



From this it is obvious that hard seeds must retain the power of 

 germination for many years, as otherwise the great object of their forma- 

 tion would be defeated. Professor Ewart has divided seeds into three 

 classes according to their duration of life. 



The Microbiotic seeds which do not live for more than three years, 

 The Mesobiotic, which last from three to fifteen years and 

 The Macrobiotic, which may retain the power of germination from 

 fifteen to over one hundred years. 



All the hard seeds are included in the last class; they remain un- 

 harmed by great extremes of heat and cold and are, in fact, the most 

 resistant of all living organisms. 



In Acacias and other allied plants the formation of hard seeds may 

 be regarded as a special adaptation to bush fires which, in previous ages, 

 were probably more prevalent in Australia than at the present time on 

 account of the numerous volcanic eruptions. The effect of such fires 

 would be to burn off the existing vegetation and the humus on the surface 

 of the soil ; the seeds themselves would be saved from injury by the 

 presence of the hard covering which, however, would become wholly or 

 partially charred by the flames, thus rendering the seeds permeable to 

 water and enabling them to germinate. Any seeds which escaped charring 

 would be gradually rendered permeable by the action of the alkaline ash 

 of the humus which becomes dissolved in rain water. By this means, 

 the species is not only enabled to survive the devastation but is instru- 

 mental in replacing the vegetation of the cleared part. 



There have been several theories advanced to account for this hard- 

 ness. Percival, in his Agricultural Botany (p. 626), states that the hard- 

 ness " is due to the large proportion of ash ingredients, especially silica 

 and lime," contained in the seed coats. This theory was disproved bv 

 Leake^, who compared the proportions of ash present in the seed coats 

 of two species of Indigo plants {Indigofera arrecta and Indigofera 

 sumatrana), and found a greater quantitv present in the softer freely- 

 germinable variety (/. sumatrana). Later, Jarzymowski^ suggested that 

 the hard'-'ess was probablv due to the small size of the cell cavity of the 

 outer palisade cell covering the seed, but Bergtheil and Day^ mnde com- 

 parisons between the cells of the above-mentioned seeds and found no 



1. Journ. Roy. Hort. Soc, Vol. XXIX. 2. Inauqural DUxertation, Halle, 1905. 3. Annals of 



Botany, Vol. XXI, 1907. 



