Longevity of Seed/^. 205 



mentfi. It appeared to be in this ecl;jre that the extreme iiu- 

 I>erineability of the seed coat was located. 



The vaa'iatinns in tlie resisting powers of the different seeds 

 are very curious, and as will be notict'd in the accompanying 

 tables, the thickness of the cuticle dues not seem to be solely 

 responsible in determining the powers of resistance to swelling. 

 Naturally the quality and degree of impregnation of the cuticle 

 is as important as its thickness. As an example of this a few 

 cases of different species of Acacia may be cited. 



Thus the thickness of the cuticular layer of Araria diffusa, as 

 measured by the eyepiece micrometer was .042 mm., whilst that 

 of Araria r/Iauce.scens was .022 mm. In the former case soaking 

 for 0.5 hnurs in acid was sufficient to produce swelling of 

 the seeds when put into waiter ; but in the latter case none of the 

 seeds swelled in water unless they had been previously soaked in 

 sulphuric acid for l.o hours. 



As a general nile in small and medium-sized seeds, the cuticle 

 is well developed, and represent?; the impermeable part of the 

 seed coat, while in the case of large seeds, such as those of 

 Adansonia Greyorii, Mucuna yigantea. Wistaria Maiden- 

 iana and Guilandina BondurelTa, the cuticle is relatively unim- 

 portant and inconspicuous. In these seeds the extreme resist- 

 ance which they exhibit appears to bo located in the palisade 

 cells. The above conclusions were arrived at as a result of 

 further experiments which were carried out with the seeds. 



The unswelled seeds, after several days' soaking in water, were 

 placed in strono: sulphuric acid and left there for about 15 

 minutes. They were removed, and again placed in water, in 

 which they remained for a day. Immersion for 15 minutes in 

 nearly every case proved to be insufficient to render them per- 

 meable, and conseqtiently they were replaced in the sulphuric 

 acid for 10 or 15 minutes again. Half an hour's immersion in 

 the acid v;as found to be adequate for most of the seeds, there 

 being a small minority which required further soaking in acid 

 for 15 to 60 minutes longer. The minimum times required for 

 the different varieties of seeds to be soaked in acid before they 

 are capaible of imbibing water are stated in the accompanying 

 tables. Directly a seed was seen to have swelled in water, a 

 section of the seed coat was cut, with the result that in the 



