50 



GROWTH OF PLANTS 



more, but the seeds best adapted for long life in the soil are certain hard 

 seeds, i.e., seeds that do not absorb water. This is true only if the hard 

 coats offer great resistance against softening in the soil. The most striking 

 example of this is the old seeds of the East Indian lotus (Nelumho nucifera) 



m — ii 



NEW 



OLD 



mm: 



B 



Figure 16. A, Relative rate of growth of freshly-harvested and century-old seeds. 

 Coats must be broken to permit water absorption and germination. B, Structure of 

 coats showing water-resistant layers. The water-resistant layers are (a) epidermis, and 

 (6) outer end of palisade layer, down to (m) the "light line." C, 30-60 ft. bank left by 

 the cut of the river. Seeds located in strata 3-6 ft. from top of this precipice. D, Plant 

 grown from one of the old seeds. 



that Ohga ^^ dug from a naturally drained lake bed in Manchuria. He 

 offers evidence that these seeds, many of which were still hard and 100 per 

 cent viable, had been in the soil for two centuries or more. Fig. 16 shows 

 the vigor with which the old seeds germinate when the coat is made per- 

 meable by sulfuric acid treatment, also the several layers of the seed coat, 

 indicating the parts that prevent water absorption. In the old seeds that 

 had been in the soil the epidermis and much of the outer end of the pali- 



