lo Dec, 1 910.] Tlie Nature and Uses of Hard Seeds. 775 



large seeds, whereas for small seeds the other methods are more effective. 

 If the cuticle is broken at any one point, water will enter and spread to 

 all parts of the seed, so a single scratch which passes through the cuticle 

 is sufficient to render a seed permeable. The scratching is performed by 

 a file in the case of large seeds, or in the smaller ones, by treating the 

 seeds with hard sand either by shaking them up with it or by passing 

 them through revolving cylinders lined with cement in which the sand is 

 embedded. Another method for removing cuticle is to treat the seeds 

 with some strong corrosive agent such as concentrated sulphuric acid and 

 if the treatment is sufficiently prolonged, the cuticle will be completely 

 removed. Fig. d shows a portion of the seed coat of Blackwood after 

 treatment of this kind and if this be compared with Fig. c, it will be seen 

 that in the former (d), the cuticle is entirely gone and the ends of the 

 palisade cells are exposed on the surface ; such a seed would now swell 

 readily if placed in water. The duration of treatment required to remove 

 a cuticle varies from fifteen minutes to several hours according to the 

 resistance of the seed. As has been already indicated, similar results may 

 be obtained by charring or by the action of alkalis. 



The second method, \\z. that of extracting the waxy substances from 

 the cuticle is perhaps of scientific rather than commercial importance. 

 The seeds are treated with certain chemicals which are recognised fat 

 solvents such as chloroform, ether or hot alcohol, but of these I found 

 chloroform to be the most effective. The duration of treatment required 

 again varies but is usually from three to four months. At the end of 

 that time sections stained and compared v.ith similar preparations of un- 

 treated seeds show a marked contrast, which can, perhaps, be best appre- 

 ciated by comparing Figs, f and g. These are sections of the seed of 

 Bottle-brush Wattle before and after treatment, and it will be noticed 

 that all the parts which in f were stained dark brown, are of a reddish 

 colour in g. 



Figs, a and b are of treated specimens of Indigofera arrecta and 

 Cytisus albiis respectively, and, in these, the outer layer only was 

 cuticularised. Fig. e is of special interest, as it represents a different type 

 of seed coat. It is the seed of a Melilot {Melilotus albus) often called 

 Bokhara Clover. In it, the outer membrane is not cuticularised but only 

 the ends of the palisade cells. This figure was made after prolonged treat- 

 ment with chloroform and the dark coloured ends of the cells are the 

 parts which gave the cuticular reaction in the untreated seeds. I am led 

 to believe that, in this case, the function of the outer membrane is to act 

 as a kind of cement substance which holds the cuticularised ends of thQ 

 cells closely together, and .so prevents water from pu.shing its way in 

 between them. The last Fig., h, shows a section of the treated seed coat 

 of Canna indica, after long soaking in chloroform; in this, all the thickened 

 cell-wall now- coloured blue was completely cuticularised in the original 

 seed. 



The common practice of soaking hard seeds in hot water to make 

 them swell may be explained in the following way. The effect of the 

 heat is to melt the particles of w^ax which are distributed through the 

 wall. When they are melted they will tend to run together to form larger 

 isolated drops and, in this way, spaces will be left through which the 

 molecules of water can push their way into the seed causing it to swell 

 and germinate. 



15937. 2 D 



