402 BerfhiiRees: 



Structure of Seed Coat and Resistance 

 to Water. 



As has been already mentioned in the introduction to this 

 paper, Dr. White examined more than 60 kinds of hard seeds, 

 and found that in every case the seed was covered by a cuticle 

 which rendered it impermeable to water. This cuticle stained 

 brown with chlor-zinc-iodine. 



In this work I have examined an additional number of seeds, 

 and have selected six kinds, the seed coats of which differ some- 

 what in structure. These have been used throufrhout as types 

 and subjected to various treatments, in order to determine the 

 detailed microscopical structure of the impermeable coat or 

 coats, the nature and distribution of the impregnating sub- 

 stances, and the character of the material forming the basis of 

 the cuticularised walls. In each case a large number of seeds 

 were soaked in water for forty-eight hours, and all those which 

 remained unswollen after that time were picked out and set 

 aside for further treatment. In the first place hand sections 

 of the seed coats were cut and stained on the slide with chor- 

 zinc-iodine, and in this way all the cuticularised portions were 

 clearly differentiated. The thickness of the cuticle was also 

 measured. The seeds were then treated with strong sulphuric 

 acid for short periods of time, well washed and soaked in water 

 for twenty-four hours between each application. As soon as a 

 seed was seen to swell hand sections were cut, stained and 

 examined, and compared with those of the untreated seeds. In 

 this way it was possible to determine the smallest amount that 

 must be removed from the coat to enable water to enter the 

 seed, and hence to determine the internal boundary of the im- 

 permeable covering. 



In many cases the water appeared to enter at one point, and 

 gradually pass to the rem.aining portion of the seed, causing it 

 to swell also. This was, of course, most noticeable in the larger 

 seeds, and in such cases the sections were cut from the part that 

 swelled first. 



The seeds seleeted for this special treatment were Indigofera 

 arrecta, Cyttsus albus, Acacia melanoxylon, Melilotna alba, 

 Alhizzia lophantha and Canna indica. 



