Longevity of Seeds. 403 



Iiidigofera arrecta. — The minute structure of the coat of this 

 seed has already been described by Bergtheil and Day, who 

 found a membrane to be present which stained with phosphoric 

 acid and iodine, but not with chlor-zinc-iodine, and thence con- 

 •cluded that the membrane was not the same as ordinary cuticle. 

 With carefully prepared chlor-zinc-iodine, however, I was able 

 to obtain the ordinary staininir results for cuticle in this case, 

 thus confirming Dr. White's results. 2 



The average thickness of the cuticle was 0.008 mm. The 

 walls of the palisade cells below the cuticle stained the purplish 

 colour of hemicellulose rather than the blue characteristic of 

 cellulose. In treating with sulphuric acid the periods were 

 rshort ones of five, ten, fifteen and twenty minutes. There is a 

 considerable variation in the resistance of the seeds to the 

 .action of the acid. Some swelled after fifteen minutes, while 

 ■others required thirty minutes or longer to make them per- 

 meable. Sections of the swollen seeds showed that the cuticle 

 had been removed by the action of the acid, and that the ends 

 of the palisade cells were exposed on the surface. (Fig. 79 [3].) 

 Sections for comparison were also made from a more resistant 

 seed, which remained unswollen in water after previous treat- 

 ment with the sulphuric acid for a corresponding period. In 

 this the cuticle was still visible as a continuous layer, but was 

 reduced to about one-third of its original thickness. (Fig. 79 

 [2].) From this it is evident that the resistant powers of this 

 seed are due to the cuticle only, and that the inner layer is as 

 impermeable as the outer, and that the whole layer must be 

 removed in order to allow water to pass readily through the 

 palisade cells and to enter the seed. 



Cytisus alhus. — The structure of the coat (Fig. 79 [4]) is 

 practically the same as that of Indigofera arrecta except that 

 the cuticle is only half the thickness of that of the latter seed, 

 being 0.004 mm. in thickness. The seeds were treated with 

 sulphuric acid for five, ten, fifteen and twenty minutes. There 

 was some variation in the length of treatment required, but the 

 average time was fifteen minutes, which was shorter than the 

 Average for seeds of Indigofera arrecta. This was only to be 



1 .\nii. Bot., vol. xxi., Jan., 11)07. 



2 Proc. Roy. Soe. Victoria, vol. \\i., pt. i. 



12a 



