404 Bertha Mees : 



expected, as the seed ooats were so much alike in structure, 

 and those with a thicker cuticle naturally required longer treat- 

 ment. Sections of the swollen seeds showed that the cuticle 

 alone had been removed by the acid, and that the palisade cells 

 were intact, so that in this type also it is the cuticle alone which 

 confers impermeability on the seed. 



Aran a ineJanrkvylon. — These seeds are also covered by a layer 

 of cuticle which is much thicker than in either of the preceding 

 types, being 0.013 mm. (Fig. 79 [5].) Tlie walls of the palisade 

 cells are of cellulose, and not hemicellulose, as was the case with 

 the majority of seeds that I examined. As this cuticle was 

 thicker than the others the periods of treatment were corres- 

 ponding longer, and it was found, instead of swelling in water 

 after about fifty minutes, as might have been expected, it was 

 only after one hour and twenty minutes tbat they became per- 

 meable. Microscopic exauiination showed, as in the previous 

 cases, that the cuticle only was gone, and that the palisade 

 cells were unchanged, so it seems safe to conclude that the 

 cuticle is of a more resistant nature than that of Cytisus al- 

 bus or of Indigofera arrecta. 



Me/ Hot us alba. — The seed coat in this case is of an entirely 

 different type. The outer layer consists, like the others, of 

 l^alisade cells covered externally by a structureless membrane 

 which, however, did not ajjpear to be cuticle but hemicellulose. 

 It stained majenta with chlor-zinc-iodine. To confirm this result 

 I tested similar sections with ])hosphoric acid and iodine, and 

 also with chlorophyll, but in no case did the outer membrane 

 give the cuticle reaction. 



With I'egard to the palisade cells themselves the greater part 

 of the wall appeared to be composed of hemicellulose, and the 

 outer ends only were cuticularised and microscopic examination 

 showed the outer cuticularised ends projecting, as it were, into 

 the external hemicellulose membrane. (See Fig. 1 [6].) 



In seeds which had been soaked in sulphuric acid for twenty 

 minutes the outer membrane, and, in addition, the cuticularised 

 ends of the cells were dissolved away. Such seeds swelled 

 readily in water. In order to find whether the outer membrane 

 was in itself impermeable to water, some more seeds were 

 treated for shorter periods in order to dissolve off the outside 



