Longevity of Seeds. 413 



of the palisade cells as well, as in Alhi~:ia loplidntlia. The 

 deuree of iuipenueability does not depend onh' on the thick- 

 ness of the cuticle, but probably on the proportion of waxy 

 substance present in the membrane. 



W. The cuticle found covering hard seeds differs somewhat 

 from that existing on many leaves. In the former it is an 

 exudation beyond the cell wall, whereas in the latter it consists 

 of a definite basis throughout which the particles of cutin are 

 deposited. In a thick cuticle like that of Alhizzia lophautha 

 the greater thickness is probably due. in part at least, to a 

 greater proportion of cutin being present, so that the degree 

 of separation of the micellar basis must be greater than in a 

 thinner cuticle like that of Cytiftus alhus or Indigofera ar recta. 

 The nature of the substance forming the basis may vary some- 

 what. Judging from the seeds examined it seems, in the 

 majority of cases, to be hemicellulose ; in Canua indira it 

 seemed intermediate between cellulose and hemicellulose, and 

 in one case (Acacia melanorylon) it was made up of pectose, and 

 in this la«t case the cuticle was, curiously enough, of a more 

 resistant nature than that of those which had a basis of hemi- 

 cellulose. 



EXPLANATION OF PLATES. LXXIX.— LXXXL 



Plate LXXIX. 



Fig. L — Seed coat of Indigofera arrecta. 



Fig. 2. — Same after short treatment with sulphuric acid. 



Fig. 3. — Same after longer treatment \yith sulphuric acid. 



Fig. 4. — Seed coat of Cytisus albus. 



Fig. 5. — Seed coat of Acacia melanoxylon. 



Fig. 6. — Seed coat of Melilotus alba. 



Fig. 7. — Same after treatment with sulphuric acid. 



Plate LXXX. 



Fig. a. — Seed coat of Albizzia lophantha. 



Fig. b. — Same unswollen after treatment with sulphuric acid. 

 Fig. c. — Same swollen after pi'olonged treatment with Ht,, SO^. 

 Fig. d. — ^Seed coat of Canna indica. 



